Introduction

As with many subfamilies that comprise the Acrididae, the Catantopinae have had a rather inconstant taxonomic past. Questions regarding membership, their nearest relations, and monophyly are far from settled. Some orthopterists (e.g., Bellman & Luquet 1995; Huo et al. 2007; Li et al. 2011) continue to adhere to Dirsh's (1975) system of clumping together and assigning subfamilies Calliptaminae, Catantopinae, Cyrtacanthacridinae, Eyprepocneminae and Oxyinae, among others, to the family “Catantopidae”. This construct was adumbrated earlier by Mishchenko (1952) who divided the assemblage into more or less the same subsets, tribes in this case. Many of the latter are now regarded as bona fide subfamilies of Acrididae as documented in the current Orthoptera Species File (OSF — Eades et al. 2013). Various components of Catantopinae's contorted history are described by Vickery and Kevin (1985), Song and Wenzel (2008), and Li et al. (2011). The latter correctly points out that questions of relationship and monophyly cannot suitably be addressed without a proper phylogeny. The only extensive morphology-based phylogeny of Catantopinae appeared just recently (Li et al. 2011), but, as will be discussed later, findings are not entirely clear. Previously, small numbers of Catantopinae had been included in a few morphological studies in which the primary goals focused on the evolution of specific traits rather than on phylogeny (Eades 2000; Song & Wenzel 2008).

Analysis of DNAsequences has not been particularly illuminating either. Given the large number of catantopines worldwide (Otte 1995), there have been surprisingly few molecular phylogenetic studies of the subfamily. Within the past 6 years, about 10 reports have appeared which examine relationships among the aforementioned subfamilies, including Catantopinae. A major shortcoming of these studies is that only 3 or fewer catantopine genera were included. In fact, in some cases (e.g., Zhao et al. 2011), genera labelled as Catantopinae are instead members of the Melanoplinae. Sun et al. (2010) did publish the complete genome of a supposed catantopine, Primnoa, but it too turns out to be a melanopline, according to the OSF.

The aim of this note is to revisit questions of monophyly and relatedness among a somewhat greater sampling of the Catantopinae (sensu OSF) than that previously undertaken. From the outset it should be stated that by no means is this study exhaustive or to be viewed as definitive, given the relatively small number of taxa and tribes sampled. Nevertheless, it does represent one of the first studies that focuses primarily on the phylogenetics of the subfamily itself (sensu OSF).

Materials and methods

Species, along with sources, geographical ranges and subfamilial affiliations (sensu OSF) are listed in Table 1. Of the subfamily's 18 tribes, 3 are represented here; one genus, Apalacris, is unassigned. Three genera are restricted to Australia; the rest are more widely distributed in the Old World. Representatives of Calliptaminae, Cyrtacanthacridinae, Eyprepocneminae, Melanoplinae and Oxyinae are also included. Pyrgomorpha served as the outgroup.

This investigation was based on sequences obtained from specimens sent to this laboratory by colleagues; other sequences (those of the first 6 taxa and Oxya), were obtained from GenBank. DNA samples analyzed in this laboratory were extracted from specimens using a QIAGEN DNeasy tissue kit (Mississauga, Canada). Portions of the mitochondrial genes encoding cytochrome oxidase subunits I (CO 1) and II (C02), cytochrome b (cytb) and NADH dehydrogenase subunit V (ND5) were amplified and sequenced. Primer sequences, PCR gene amplification conditions, as well as DNA sequencing methods, are described elsewhere (Litzenberger & Chapco 2001a, 2001b; Contreras & Chapco 2006).

Sequences were easily aligned by visual inspection, transferred into MacClade (Maddison & Maddison 2004) and analyzed using the software packages PALIP* (version 4.0b8 - Swofford 2003) and MrBayes (Version 3.2 - Ronquist et al. 2011). Both standard maximum parsimony (MP) and weighted parsimony (wMP), as described by Farris (1969), were conducted. Searches were repeated using all substitutions at the first 2 codon positions but only tranversional substitutions at the third position (methods referred to as MP123TV and wMP123TV, respectively). All (heuristic) parsimony searches employed the TBR branch-swapping option with 10 random addition replicates. Bayesian analysis applied default settings with respect to prior distributions, number of chains, start trees, etc. Eight Monte Carlo Markov chains, 1 cold and 7 heated, were run simultaneously for 50 million generations when convergence had been attained. Trees were sampled every 500 generations; consensus of the last 10000 trees was calculated. Data were partitioned according to codon position and gene; each partition was allowed to follow its own GTR + G + I evolutionary model. Levels of support for parsimony-derived relationships were estimated through 1000 bootstrap replicates. Maximum likelihood procedures were not performed owing to the excessive run-times that would be required for bootstrapping. For Bayesian analyses, measures of nodal support appeared in the form of posterior probabilities (PP). For all analyses, the 4 sequences were treated as a combined unit, a procedure that, as in our previous studies, always yielded trees with greater resolution and support when compared to those based on single genes.

Table 1.

Species analyzed, locations and GenBank Accession numbers of mtDNA sequences.

Results

Sequences analyzed here are devoid of inserts and/or deletions and are indeed believed to be mitochondrial and not nuclear pseudogene inserts. Moreover, the sequences adhere to other criteria set out previously by Zhang and Hewitt (1996) for ensuring that they are mitochondrial.

Of the different parsimony searches, wMP123TV yielded tree with the greatest resolution, presented as a bootstrap consensus tree in Fig. 1. In general, very similar relationships were uncovered by the Bayesian method (Fig. 2). Members of Catantopinae, singly or in groups, are located in 5 areas of both trees. At the tree's apex, 6 catantopines form a clade, 5 belonging to the tribe Catantopini. In a second location, Pezotettix (tribe Pezotettigini) is tightly linked to a member of the subfamily Eyprepocnemidinae; together they are basal to the above sextet. Another group of catantopines, external to the aforementioned, consists of the Australian trio: Coryphistes, Goniaea, Theomolpus. Although the cluster has excellent support, their inter-associations differ between the 2 trees. The phylogenetic position of Traulia (tribe Trauliini) is unclear. In the parsimony tree, the genus has a moderately strong association with Calliptamus, whereas in the Bayesian tree it is as part of a polytomy at the crown end. Sphenophyma is the first catantopine to diverge, occupying a position at the tree's base. It belongs to the tribe Pezotettigini but is distant from the latter's only other member, Pezotettix.

Among the other subfamilies, members of Oxinae and Melanoplinae are nextto diverge after Sphenophyma. The Calliptamus branch follows, but as stated above, it is linked with Traulia in the parsimony tree; in the Bayesian topology it appears alone. With respect to the 2 members of the Cyrtacanthacridinae, parsimony analysis places the pair at the base of the crown sextet plus Platyphyma-Eyprepocnemus and inside the Australian group, albeit with weak support. In the Bayesian tree, the pair is part of a large polytomy as seen in Fig 2.

Discussion

Clearly, the subfamily Catantopinae (and the 2 tribes Catantopini and Pezotettigini for that matter) cannot be regarded as monophyletic. Historically, Catantopinae have been variously labelled as “le groupe artificiel” (Amédégnato 1974), a “heterogeneous group” (Song & Wenzel 2008; see also Dirsh 1975) and — owing to its variability — a subfamily that “should be subdivided” (Vickery 1997). Lack of monophyly had already been inferred by Ma et al. (2006), Wang et al. (2008) and Liu et al. (2008); however, fewer taxa and shorter DNA sequences were analyzed and branch support values on the whole were low. Curiously, Li et al. (2011) in their morphological study claimed that 4 of the 7 subfamilies of Catantopidae are monophyletic, including Catantopinae. Yet this is clearly not the case, which even a cursory examination of their trees should reveal. Catantops, Stenocatantops and Xenocatantops do indeed cluster together as they do here, but other catantopines in their study, such as Pachyacris, Ecphanthacris, Fer and Bannacris, are sprinkled throughout their topologies.

Catantopinae can be added to a seemingly growing list of other subfamilies recently deemed to be non-monophyletic: Acridinae, Gomphocerinae and Oedipodinae (Chapco & Contreras 2011), and perhaps Melanoplinae (Chintauan-Marquier et al. 2011) but not, apparently, Cyrtacanthacridinae (Song & Wenzel 2008) or Proctolabinae (Rowell & Flook 2004). As expressed by Key and Colless (1993) [see also Amédégnato 1993; Rowell 2005], many traits commonly used for taxonomic purposes are particularly subject to evolutionary convergence (e.g., by “tracking” environmental changes) and may, for some reason, be more common in orthopteran insects than previously acknowledged.

It is difficult to compare the present findings with those in the literature owing to the spotty occurrence of catantopines in those works. A few points of interest warrant mention however.

The crown clade.—The linking of Catantops and Xenocatantops mirrors the morphological results of Li et al. (2011) and molecular findings of Wang et al. (2008). With respect to the tribally unassigned Apalacris, both studies position the genus far from the aforementioned pair (see also Liu et al. 2008), albeit with low bootstrap support. Mishchenko (1952) placed Apalacris within the tribe Coptacrini, which has since been elevated to a subfamily of Acrididae (Coptacridinae). There may indeed be some support for an association with the latter if the morphology-based phylogeny derived by Li et al. (2011) is upheld by comprehensive molecular studies in the future. [It should be noted that the analysis of a short segment of the C02 gene by Ma and Huang (2006) also suggested an association with the Coptacridinae]. It will, therefore, be interesting to see if including Coptacridinae sequences will alter the current placement of Apalacris.

Traulia.—The obvious lack of affinity between Traulia and other members of the Catantopinae, appears to agree with the findings of Eades (2005) and Liu et al. (2008) who, respectively, examined orthopteran phallic anatomy and mitochondrial ribosomal sequences. The genitalic anatomy of Traulia is shown to be quite different from that of other catantopines; instead, structures appear to resemble those of the Oedipodinae to which Eades contemplates making a possible taxonomic shift. Liu et al. (2008) also distanced Traulia from other catantopines, but unlike Eades, discovered that it was far removed from the oedipodines (see also supporting molecular evidence by Zhao et al. 2011 ). In any case, it is presently uncertain where Traulia belongs.

Pezotettix and Sphenophyma.—Both belong to the tribe Pezotettigini, which evidently is not monophyletic. There is very little mention of these genera in the molecular literature apart from the use of the Pezotettix as an outgroup in 2 studies (Hochkirch & Görzig 2009; Chintauan-Marquier et al. 2011).

Sphenophyma is currently geographically restricted to Asia Minor (Fishelson 1985) and is the first genus to diverge from the common ancestor of the entire body of taxa studied. This region may have been the place of origin for these subfamilies whose antecedents dispersed from there. Another plausible scenario is that the common ancestor was widespread and some elements evolved into the present day, range-limited, Sphenophyma. Other ancestors gave rise to, in turn, Oxynae, Melanoplinae, and so on (see Figs for branching sequences).

The Australian genera.—It is interesting that the 3 Australian genera analyzed here do form a clade, but given this miniscule sample it is impossible, although tempting, to make any inferences about their biogeographical origins.

Relationship among the “spine-throats”.—After the divergence of Sphenophyma, the temporal sequence of branching of the other subfamilies (some scattered among the catantopines) appears to be: Oxyinae, Melanoplinae, Calliptaminae, Cyrtacanthacridinae and Eyprepocnemidinae. This sequence is somewhat similar to the branching order discovered by Liu et al. (2008) and Zhao et al. (2011) who, respectively, analyzed sequences of 12S+16S rDNA and those of the mitochondrial control region (see also Rowell & Flook 1998 who also included 18S sequences). In all investigations, Catantopinae is shown to be more closely related to the Cyrtacanthacridinae than either is to Melanoplinae or Oxyinae. With respect to the position of Calliptaminae, present results agree with those of Rowell and Flook (1998) but not with the findings of Zhao et al. (2011). Of the 3 papers, only Rowell and Flook include Eyprepocnemidinae and here it occupies an unresolved position relative to the other subfamilies.

Based on this admittedly limited study, it can be stated that Vickery's (1989) suggestion that Catantopinae should be subdivided rings true. Clearly much more work needs to be done to discover what those dividing lines should be.

Fig. 1.

Bootstrap consensus tree recovered using weighted maximum parsimony. Substitutions at the first 2 codon positions and transversions at third codon positions were scored. Numbers (> 50 %) indicate bootstrap levels of support using 1000 replicates.

Fig. 2.

Bayesian tree. Data were partitioned according to codon position and gene; each partition was allowed to follow its own GTR + G + I evolutionary model. Eight Monte Carlo Markov chains, 1 cold and 7 heated, were run simultaneously for 50 million generations when convergence had been reached. Trees were sampled every 500 generations; consensus of the last 10000 trees was calculated. Posterior probabilities (> 50%) are indicated in the figure.