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The effects of aquatic deposition of coal combustion residues (CCRs) on amphibian life histories have been the focus of many recent studies. In summer 2005, we raised larval Southern Leopard Frogs, Rana sphenocephala, on either sand or CCR substrate (approximately 1 cm deep within plastic bins) and documented effects of sediment type on oral disc condition, as well as time to, mass at, and total body length at key developmental stages, including metamorphosis (Gosner stages [GS] 37, 42, and 46). We found no significant difference in mortality between the two treatments and mortality was relatively low (eight of 48 in the control group and four of 48 in the CCR group). Ninety percent of exposed tadpoles displayed oral disc abnormalities, while no control individuals displayed abnormalities. Tadpoles raised on CCR-contaminated sediment had decreased developmental rates and weighed significantly less at all developmental stages, on average, when compared to controls. The CCR treatment group was also significantly shorter in length than controls at the completion of metamorphosis (GS 46). Collectively, these findings are the most severe sub-lethal effects noted for any amphibian exposed to CCRs to date. More research is needed to understand how these long term effects may contribute to the dynamics of local amphibian populations.
Caudal autotomy is a widespread antipredator mechanism among lizards. Thrashing the tail distracts the predator's attention, facilitating the lizard's escape. Regeneration occurs rapidly, but the regenerated tail differs from the original in many ways. In the present study, we examine probable physiological differences between, and the performance of, regenerated and original tails in Aegean Wall Lizard from Aegean islets. Autotomy was induced artificially. There was no difference in duration of tail movement. Moreover, we failed to detect any differences in lactate and glycogen concentrations. Differences in LDH activity and protein levels were not significant. However, lipid levels were higher in regenerated tails. Finally, regenerated tails show higher autotomy percentages when predation was simulated. We failed to detect large-scale physiological differences in regenerated tails (with the exception of lipids) in these particular populations.
Hisonotus armatus, a new hypoptopomatine species, is described from the Laguna dos Patos basin, Rio Grande do Sul State, southern Brazil. The new species is distinguished from other Hisonotus species by aspects of the morphology of the rostral plate, the arrangement of abdominal plates, and the caudal-fin color pattern.
Hisonotus armatus, nova espécie de hipoptopomatíneo, é descrita do sistema da laguna dos Patos, Rio Grande do Sul, sul do Brasil. A nova espécie se diferencia das demais do gênero Hisonotus pela morfologia da placa rostral, pelo arranjo das placas abdominais, e pelo padrão de colorido da nadadeira caudal.
North-to-south clinal variation in morphology is described in Arthroleptis affinis of the Eastern Arc mountains of Tanzania. While northern populations are readily separable from other Arthroleptis species, southern populations are not. This complicates differential diagnosis. Despite this, it is concluded that in the present state of knowledge, it is more useful to include the clinal variation under the name A. affinis, rather than attempt to divide the species into groups that defy clear morphological definition.
Prey that are cryptic when at rest should limit movement to avoid disrupting crypsis. We studied effectiveness of crypsis and degree of reliance on immobility versus escape by Craugastor frogs approached by a predator. We studied detectability of C. fitzingeri resting in a 2 m diameter circle of leaf litter using four human observers. Nearly 40% of frogs were not detected within 60 s, and mean detection time was more than 30 s despite a small search area. Given a much lower density in natural habitats, it is likely that these frogs are rarely detected visually without area-concentrated search, except perhaps by predators sensitive to wavelengths not detected by human beings. When approached by a human, over 90% of individuals belonging to five species of Craugastor remained immobile until the predator reached them. Only C. noblei fled, and this species fled more frequently than the others at higher approach speed. Approach speed did not affect probability of jumping or distance jumped. Distance jumped varied among species, but was unrelated to body length except for C. mimus during fast approaches. Extreme reliance on crypsis reinforced by immobility suggests that crypsis is so effective in these frogs that survivorship may be higher for individuals that do not attempt to escape. The increased probability of being detected and attacked upon moving combined with limited escape capacity presumably raises the probability of being captured for frogs that jump. The importance of crypsis is emphasized by observations that almost all frogs that jumped reestablished crypsis after a single jump by becoming immobile, and some burrowed into leaf litter upon landing, concealing the head and part of the body.
Painted Turtles (Chrysemys picta) are often used to test life-history theory. However, within populations, the factors that contribute to among-individual variation in egg size and clutch size are poorly understood, and an understanding of the biotic and abiotic parameters that contribute to this variation is important when framing patterns of maternal investment in a life-history context. We examined proximate sources of reproductive variation in a northern population of Painted Turtles, we attempted to frame these sources of variation in a life-history context, and we evaluate which optimality model most adequately explains patterns of reproductive allocation in populations of small-bodied turtles. We used multiple linear regression on data from 168 first clutches of marked females that nested at a long-term study site in Algonquin Park, Ontario, Canada, in 2004. We found that mean egg mass was positively related to maximum plastron length (MPL) and female age, and negatively related to clutch size and water temperature prior to oviposition. Clutch size was positively related to MPL and carapace height, and negatively related to mean egg mass, and the number of clutches laid in the season. Body size (MPL) was the most important predictor of each reproductive parameter, and residual analysis indicated that egg mass was more conserved than clutch size across the range of female body sizes sampled in this study. Thus, egg size may be optimized as a body size-specific function, and in light of this, we suggest that ‘phenotype-habitat matching’ may occur in C. picta. If a female's phenotype (e.g., body size) influences the selective environment of her eggs and hatchlings (e.g., if larger females generally nest farther away from water), then the optimal strategy of maternal investment should vary among maternal phenotypes. The positive correlation between egg mass and body size that was observed in the present study can be explained in adaptive terms under hypotheses based on the concept of phenotype–habitat matching.
The systematics of the abyssal giant cusk-eel genus Spectrunculus was revised, based on the examination of 55 specimens recently collected from the northern Mid-Atlantic Ridge and 32 specimens from earlier collections in the Atlantic and Pacific Oceans. The conclusion of Nielsen and Hureau that only one sexually dimorphic species, S. grandis, exists, is rejected. The examination of meristics, external and internal morphometric characters, and body coloration allows the distinction between two species, requiring the resurrection of S. crassus. The major diagnostic characters are: number of dorsal-fin rays (135–148 in S. grandis vs. 121–139 in S. crassus), anal-fin rays (101–112 vs. 91–102), total vertebrae (77–88 vs. 71–78), otolith ostium depth in percentage of sulcus length (19–29% vs. 30–40%), and maximum standard length (<130 cm vs. <60 cm). In the North Atlantic S. crassus is most often darker than S. grandis, but because many exceptions exist, coloration proved an unreliable diagnostic character. The results are discussed with respect to evolution and ecology of two abundant sister species co-occurring in the lower bathyal and abyssal zones.
Corumbataia veadeiros, new species, is described from the upper Rio Tocantins basin at the Chapada dos Veadeiros formation, Goiás State, central Brazil. The new species is distinguished from all other species of Corumbataia by its lack of a raised tuft of enlarged odontodes on the supraoccipital, an infraorbital canal entering the infraorbital series via the sphenotic, and by the color pattern of the caudal fin, which is composed of vertical dark bars.
We used DNA sequences from several mitochondrial regions (ND2, ND4, and adjacent tRNAs) to examine genetic structure and divergence among populations of the Striped Plateau Lizard, Sceloporus virgatus. In the northern portion of this species' range, populations occupy mesic habitats at higher elevations in the mountain ranges of the Madrean Archipelago, and are thus isolated by dry, inhospitable valleys. High genetic differentiation among four of these ranges, and low genetic variation within ranges, imply that gene flow among them has been limited and isolation is ancient, having occurred hundreds of thousands or even millions of years ago. These results conflict with expectations derived from geographical and paleontological data that indicate ecological conditions favoring gene flow occurred as recently as 11,000 years ago.
Hemigrammus silimoni is described from the Rio Juruena, upper Rio Tapajós basin, Mato Grosso State, Brazil. The new species is distinguished from all congeners, and in fact from the remaining Characidae, by the autapomorphic presence of an ocellus-like blotch on the caudal-fin dorsal lobe. The high level of fish endemicity in the Rio Juruena (upper Rio Tapajós basin) is discussed.
Descreve-se Hemigrammus silimoni, uma nova espécie do Rio Juruena, bacia superior do Rio Tapajós, Estado de Mato Grosso, Brasil. A nova espécie apresenta uma mancha elipsóide similar a um ocelo no lobo superior da nadadeira caudal, uma característica autapomórfica que a distingue de todas as demais espécies do gênero e mesmo de outras espécies de Characidae. O alto grau de endemismo de peixes no rio Juruena (bacia do alto rio Tapajós) é discutido.
Understanding the proximate mechanism for seasonal modulation of the adrenocortical stress response is an important step in determining the evolutionary significance of such modulation. In vitro studies of adrenocortical cell function in Eastern Fence Lizards (Sceloporus undulatus) have partially explained the mechanism for seasonal changes in male stress responsiveness, but studies of free-living females have not been conducted. Here we test two predictions generated from the in vitro work in free-living female fence lizards: the plasma corticosterone response to adrenocorticotropic hormone injection will be weaker in the postbreeding than the breeding season, and baseline corticosterone levels will be lower in postbreeding than breeding females. Twice during the breeding season and once during the postbreeding season, corticosterone concentrations were measured at capture then again after adrenocorticotropic hormone injection and one hour of confinement. Females robustly responded to adrenocorticotropic hormone, but there was no detectable seasonal difference in the strength of the corticosterone response. Similarly, corticosterone responses did not vary seasonally in females subjected only to confinement without injection. However, as predicted, baseline plasma corticosterone levels were lower in the postbreeding than the breeding season. Plasma triglyceride concentrations varied with season as well as being negatively associated with baseline corticosterone levels. The whole-organism corticosterone response may differ from that of isolated adrenocortical cells which are not subject to either paracrine or upstream hypothalamic and pituitary signals. The mechanism of adrenocortical modulation and its evolutionary significance is most likely to be deciphered by conducting studies at multiple levels of organization.
We examined the phylogeography of the Least Brook Lamprey (Lampetra aepyptera) to recognize phylogenetically distinct clades within this species and to estimate the relative contributions of vicariance and dispersal to the distribution of genetic variation. A combined data set from mitochondrial ND3 and control region sequences identified 23 unique haplotypes among 21 populations. Eleven highly differentiated clades within L. aepyptera were detected. Their distributions correspond to different drainages and/or locations within drainage. Clades differed by an average of 4.5% (range 2.5–9.0%) sequence divergence. Only two haplotypes were shared among any populations. Considerable differentiation among adjacent drainages and limited sharing of haplotypes suggested little historical or contemporary gene flow. Although clades were highly differentiated, resolution of clade relationships was limited. The presence of highly differentiated clades in different drainages suggests that vicariance has had a profound effect on the distribution of genetic variation in L. aepyptera. The lack of resolution of clade relationships within this species suggested a single event that simultaneously isolated many of these populations. Rising sea levels causing a marine incursion into the Mississippi embayment during the Pliocene could have been such an event.
Some unisexual invertebrates engage in low levels of sex with related sexual species, and this raises the possibility that unisexual vertebrates have a similar capability. In this study, I compared the population genetic signatures of a triploid population of unisexual salamanders in the genus Ambystoma and sympatric sexual A. jeffersonianum to investigate the degree to which clonal reproduction is occurring in this natural unisexual population. Analysis of nine microsatellite loci revealed extremely high allelic and genetic diversity in both the A. jeffersonianum and triploid populations, indicating that strict clonal reproduction is unlikely to be occurring among these unisexuals. In contrast, significant linkage disequilibrium for all pairs of loci, high heterozygote excess, and large variation in FIS values across all microsatellite loci (range of FIS = −0.710 to −0.157) in the triploid population indicate that gynogenesis is the most common but not exclusive form of reproduction occurring in unisexual Ambystoma. This study provides the best evidence thus far that unisexual Ambystoma are utilizing a complex mode of reproduction that has features of both sexual and asexual reproduction.
We describe a new species of Torrent Frog, genus Hylodes, from southern and southeastern Brazil. The new species is assigned to the Hylodes nasus species group and is characterized by large size, robust body, distinctly granular dorsolateral surfaces, absence of light dorsolateral stripes, moderate-sized fringe on the outer margin of toe V, and distinct advertisement call with long note duration. The new species is morphologically similar to Hylodes asper but is readily separated from that species by its distinct vocalization and by the shorter fringe on the outer side of toe V. Description of advertisement call and behavioral notes are provided.
We describe a new frog species of the genus Cardioglossa from the Upper Guinean forests of West Africa. Cardioglossa occidentalis, new species, is found in primary rainforests in Ghana, Ivory Coast, Guinea, Liberia, and Sierra Leone. We demonstrate that this species is morphologically and genetically distinct from C. leucomystax, the species to which these populations were previously assigned. Cardioglossa occidentalis differs from similar congeners by the following combination of markings: fusion or near fusion of all three dorsal lobes (cephalic, scapular, and lumbar); prominent white line extending anteriorly from arm terminates ventral to eye; dark mask extending posteriorly from eye continues unbroken beyond posterior border of scapular lobe; lateral body covered in very few, large dark spots rimmed with thin white. Cardioglossa occidentalis appears related to C. leucomystax, C. melanogaster, and C. schioetzi. This description brings the number of Cardioglossa species to 16.
Measuring stress in animals is an important component of many research studies, and it has traditionally been performed via sampling levels of corticosterone in plasma. A secondary, “hematological” approach used most commonly by researchers of birds, mammals, and other taxa involves evaluating leukocyte profiles from blood smears. Such research has shown that leukocytes have a characteristic response to stress, although in amphibians this phenomenon is not as well studied. In general, stress can induce a rise in the ratio of neutrophils to lymphocytes. We evaluated the hematological response of paedomorphic Mole Salamanders (Ambystoma talpoideum) to captivity stress, specifically focusing on this parameter, but also examining other white blood cell types. Individuals captured in the wild and held in captivity for ten days before sampling had significantly more neutrophils, fewer lymphocytes, and higher ratios of neutrophils to lymphocytes than those captured from the same locations and sampled within one hour. Captive individuals also had significantly higher numbers of eosinophils. These results are consistent with hematological research in birds and other taxa and highlight the utility of this approach for measuring stress in amphibians.
Sex reversal in the Lake Malawi cichlid, Metriaclima cf. livingstoni, was documented. A functional male in an aquarium was separated from three functional females by a divider of clear Plexiglas® sealed to tank walls. After the male was removed, one of the functional females developed male secondary sexual characteristics and fertilized eggs produced by the other females. In a second experiment, 6–7 functional females were placed in tanks without males. Again, sex change was noted with one of the former females fertilizing several broods.
Haplochromine cichlid fish have radiated into hundreds of species in East-African lakes, possibly driven by divergent sexual selection on body coloration. We studied the color polymorphic Lake Victoria cichlid Neochromis omnicaeruleus, in which a presumably ancestral phenotype with blue males and brown females co-occurs with two distinct classes of blotched phenotypes in both sexes. Similar blotch polymorphisms occur in other haplochromine species, and in all studied cases blotched females are much more common than blotched males. In N. omnicaeruleus, the near absence of blotched males seems to be partly due to genetic linkage to a dominant female determiner that turns blotched males into females. However, laboratory breeding suggests that blotched males should be much more common than observed. Here we studied whether differential predation on blotched males contributes to their scarcity. First, in a predation experiment with wild birds, blotched fish indeed incurred more predator attacks. Second, underwater observations revealed behavioral differences between the sexes, consistent with an additional predation risk for males. These data suggest that differential predation with regard to color pattern and sex may be an important selective force in the evolution and maintenance of this color polymorphism. However, we also carried out a population census which revealed that blotched males were rare already as juveniles. To explain the scarcity of blotched males in nature, we therefore have to invoke either selection against blotched males early in life, or a more complex genetic model. These results emphasize the need for further research on the ecology and genetics of this widespread color polymorphism in cichlid fish.
The phylogenetic relationships within the Centrarchid genus Enneacanthus and the role of regional historical biogeography in their radiation was examined. Based on complete mitochondrial (mt) control region sequences, E. chaetodon is a monophyletic taxon that is sister to an ‘E. gloriosusE. obesus’ clade. However, the current data indicate that E. gloriosus and E. obesus are not monophyletic taxa and appear to demonstrate either incomplete lineage sorting or a polyphyletic E. obesus. Based on molecular clock divergence estimates, the hypothesis of Pleistocene glacial cycles promoting speciation was not supported for either E. chaetodon or E. gloriosus, but is supported in having been a factor in the origins of E. obesus. Even though not a common force in terms of speciation, the Pleistocene oscillations do appear to have promoted subsequent diversification and dispersal (range expansion) for all three of these species.
During pregnancy, the metabolic rate of females may increase above basal levels to support metabolically active tissues and developing embryos. In mammals, this energetic cost of supporting the pregnancy (MCP) is an important component of reproductive effort, but less is known about the magnitude of this cost in ectothermic vertebrates. We estimated the metabolic cost of supporting pregnancy in a tropical viviparous snake, the Northern Death Adder, Acanthophis praelongus. We measured the metabolic rates of non-gravid and gravid females throughout gestation and following parturition. We also measured the oxygen consumption of a sample of neonates from each clutch within 24 h of birth. The metabolic rate of gravid females rose slowly during pregnancy, but was significantly elevated during the last three weeks of gestation. Considering the late term metabolism of gravid females as 100%, then the baseline metabolism of female Death Adders represented 36.6%, embryo metabolism accounted for 37.0%, and the cost of supporting the pregnancy was 26.4% of the total metabolic rate. Neonate metabolism during the first 24 h of birth was 2.9 times higher than the estimate for embryo metabolism. Thus, our results do not support the assumption that the metabolism of embryos (prior to birth) and neonates is similar in this species. Although gravid female Death Adders maintain high and constant body temperatures during late gestation, the energetic cost of supporting the pregnancy is only a minor component of the total reproductive effort for females of this species.
Accurate classification of sex is essential for life history studies. Benchmark sizes that can represent the size of either the smallest, average, or upper size limit of males in a population exhibiting secondary sexual characters (SSCs) are often used to assign sex in emydid turtles. This method may be problematic, however, as it ignores variation in SSC development and is unable to identify the sex of smaller individuals. To address these two issues, we present a method using Slider Turtle (Trachemys scripta) standardized residual scores of third foreclaw length and preanal tail length versus plastron length. The use of benchmark sizes that reflected the smallest or average size of male maturity for our population did not compromise accurate sex identification. Additionally, our method was able to accurately sex turtles that were smaller than the benchmark size. Our method has the potential to enhance demographic studies on turtles by allowing researchers to identify juvenile sex ratios.
The Wood River Sculpin, Cottus leiopomus, is endemic to the Wood River basin in Idaho and is a nongame species of concern because of its limited distribution, but the status and biological characteristics of this species were previously unknown. We collected 716 C. leiopomus from ten populations across the Wood River basin from streams with a variety of physiochemical conditions to estimate length and age at sexual maturity and other demographic characteristics. Most C. leiopomus were estimated to be age-1 (16%), age-2 (33%), age-3 (30%), and age-4 (12%); the oldest was estimated to be eight years old. Estimated total annual survival rate was consistent across all study sites, averaging 66% and ranging from 56 to 70%. Survival was positively correlated with mean stream width and negatively correlated with stream gradient, although sample sizes for these comparisons were small and we are cautious in asserting a causative effect. Sculpin reached 60 mm total length by age-2 and reached 100 mm at around age-4; the largest C. leiopomus captured was 121 mm. Sex ratio was near 50:50 for most populations and averaged 51% female across all populations. Fecundity ranged from 38 to 314 eggs and formed a linear relationship with fish length (r2 = 0.67). At the two sites where sampling occurred in the spring and maturity could be more definitively determined, almost all C. leiopomus age-3 and older were mature, regardless of gender. No age-1 fish were mature, and no age-2 males were mature, but 83% of age-2 females were mature. We estimated that females transitioned from immature to mature at about 55 mm and males at about 60 mm. These results are the first published data on the life history characteristics of C. leiopomus and provide useful information for the management and preservation of this species.
The main purpose of this study was to describe the morphology of the sperm packets produced by species in the genus Xenurobrycon. Males of the three species analyzed, X. macropus, X. polyancistrus, and X. heterodon, produce unencapsulated sperm bundles (spermatozeugmata) that are essentially identical in morphology. In longitudinal histological sections, each spermatozeugma is feather-like, with the tips of the sperm heads associated with a core that stains with the periodic acid-Schiff reagent (PAS ). As revealed by SEM, sperm heads are exposed only at the anterior end of the packet. Flagella cover the remainder of the packet and form a “tail” at the posterior end. The flagellum probably exits from a cytoplasmic collar at one side of the flattened sperm head, which tapers posteriorly. Spermatozeugmata are formed within the spermatocysts and only complete packets are released into the sperm ducts. Very few loose spermatozoa are seen within these ducts, attesting to the high degree of compactness of these sperm bundles. Insemination is confirmed in a specimen of X. macropus, whose ovary contained spermatozeugmata, demonstrating that intact packets can be transferred to the ovary by the male. A lateral flagellum, which is present in the xenurobryconin genera Scopaeocharax, Tyttocharax, and Xenurobrycon, may prove to be a synapomorphy for the entire tribe Xenurobryconini. In addition to providing information on reproductive morphology in these species, the results also demonstrate the potential use of characters obtained from such microscopic analyses in phylogenetic studies.
The strong connection between ecology and morphology in fishes predicts that ecologically relevant morphological features will change in concert with changes in habitat use and feeding ecology even over relatively short timescales following species introduction. Here, this hypothesis is tested by examining the trophic morphology of specimens of the native Tessellated Darter, Etheostoma olmstedi, collected at Catatonk Creek, Candor, Tioga Co., NY, USA, between 1961 and 2002. The collections of E. olmstedi bracket a 1980 range expansion by the non-native Banded Darter, E. zonale. Examination of the E. olmstedi specimens revealed that the length of the buccal cavity relative to body size increased following the invasion of Catatonk Creek by E. zonale. An increase in buccal cavity length (BCL) is expected to result in higher suction feeding performance measured as volumetric flow rate of water through the mouth. Such an increase in BCL may enable E. olmstedi to exert greater suction forces on prey and as a result, post-invasion E. olmstedi may be able to capture more elusive prey or to take prey from habitats with smaller substrates than pre-invasion E. olmstedi. The functional and potential ecological consequences of the increase in BCL suggest that the morphological change may be linked to a shift by E. olmstedi to more marginal habitats following the invasion of E. zonale.
Annual counts of egg masses have been promoted as an appropriate state variable for monitoring populations of some amphibian species. However, if some egg masses are not detected and detectability changes over time, the use of egg mass counts is unreliable. Variation in counts of egg masses may be indicative of variation in actual abundance or variation in detectability. I used closed capture–recapture models to estimate detection probability and evaluate potential sources of variation in the detectability of Wood Frog (Rana sylvatica) egg masses in a pond in Rocky Mountain National Park in 2003 and 2004. Model selection results and model-averaged estimates provided evidence that detection probability varied between years. However, I found no evidence of variation between observers within each year. The results of this study provide additional evidence that detection probability needs to be accounted for if egg mass counts are to be used to infer abundance and population trends in amphibian populations.
Sex differences in seasonal timing include differences in hatch- or birth-date distribution and differences in the timing of migration or maturation such as protandrous arrival timing (PAT), which is early male arrival at breeding sites. I describe a novel form of protandrous arrival timing, as a sex difference in birth-date distribution in a live-bearing fish (Dwarf Perch, Micrometrus minimus). In this species, birth coincides with arrival at breeding sites because newborn males are sexually active. A series of samples of pregnant females and young of year was collected in Tomales Bay, CA. I analyzed the daily age record in otoliths to estimate the conception date of broods and the age that young-of-year individuals were born. Males were born at a younger age than females, as indicated by the daily age record and also by the predominance of females in broods from which some young had already been born, which was a common occurrence in pregnant females with older embryos. Sex ratio of broods varied with conception date such that early-season broods were predominantly male, possibly as a result of temperature-dependent sex determination. The combined effects of the sex difference in age at birth and seasonal shift in sex ratio were to shift the mean birth date of males relative to females by five days. The most likely ultimate explanation for PAT in the Dwarf Perch is that it arises from exploitation (scramble) competition for mating opportunities among recently-born young-of-year males.
The population structure of the most widely distributed anguillid eel, Anguilla marmorata, was evaluated using a statistical analysis of total number of vertebrae. A total of 1166 specimens from 13 representative localities in the Indo-Pacific region from Réunion Island to Tahiti and from New Caledonia to Japan were examined in this analysis that also included previously published data. The specimens from Micronesia showed a remarkable difference from those collected at the 12 other localities, and those from Tahiti showed a significant difference from those collected at ten other localities, but not New Caledonia and Samoa. Furthermore, significant differences were found between the North Pacific Ocean region, except Ambon Island, and South Pacific Ocean regions and Réunion Island, while there were few differences between specimens from the Indian and South Pacific Ocean regions. It appears likely, based on this morphological analysis and the geographic range of this species, that there are at least four or more populations of A. marmorata as has been indicated previously by molecular genetic research.
In Lake Malawi cichlids, comparisons of feeding morphology have typically been performed at the genus level, with little emphasis on interspecific comparisons. Variation in jaw shape can be a powerful predictor of feeding performance and habitat preference. Jaw morphology and habitat partitioning were examined among species in the Lake Malawi rock-dwelling species complex, Tropheops. Although Tropheops species varied in a variety of craniofacial characters, lower jaw shape was the focus of this study because of its close association with feeding performance in bony fishes. Significant differences were observed among five microhabitat variables measured in situ for six Tropheops species at two field sites in southern Lake Malawi in July and August, 2001. Depth was identified as a major axis of trophic niche partitioning, and species-specific differences in lower jaw shape and foraging strategy were correlated with depth distributions among species. These data are consistent with the hypothesis that competition for trophic resources (epilithic organisms) has led to habitat partitioning and the establishment and maintenance of distinct trophic morphologies within the Tropheops species complex. Detailed morphological analyses of inter- (and intra-) specific trophic variation in Lake Malawi cichlids will likely lead to important insights into the proximate mechanisms that underlie cichlid trophic diversity.
Understanding the distribution patterns of closely related species is critical because the extent to which their ranges overlap determines the opportunity for competition and hybridization. In this study, we used museum records to determine the degree of overlap between two killifish species, Lucania goodei and L. parva, in Florida. While the broad geographic distributions and habitat characteristics are well-described, the degree of sympatry between the two species, the temporal stability of sympatric populations, and the abiotic and biotic conditions under which sympatric populations occur are unknown. Using the museum records, we identified sites where L. goodei and/or L. parva had been collected and classified sites as either L. goodei–allopatric, L. parva–allopatric, or sympatric. For sites that were sampled repeatedly over time, we determined the extent to which their status varied. Approximately 12–19% of sites where L. goodei was present were sympatric with L. parva at some point in time. However, many sympatric sites were not stable over time. Of the repeatedly sampled sites that were sympatric at some point in time, more than 50% varied between allopatric and sympatric status. Salinity also had large effects on distribution. Approximately two-thirds of sympatric sites were in fresh water, and the remaining one-third were in brackish water. As expected, the fish community varied between L. goodei, L. parva, and sympatric sites. The unique contribution of this study is that it provides the first estimate of the degree of overlap between L. goodei and L. parva and indicates which biotic and abiotic variables may account for this pattern.