The highest elevations of tropical mountains, much like oceanic islands, often support disproportionately high levels of endemism, some of which is concealed as cryptic species. In a search for additional species, we explored the chromosomal diversity of three morphologically defined species of black flies known only from the upper elevations of Doi Inthanon, Thailand's highest mountain. Analysis of the polytene chromosomes facilitated the discovery of the previously unknown larva of Simulium kiewmaepanense Takaoka & Srisuka, permitted linkage of the formal name of S. undecimum Takaoka, Srisuka & Saeung with its previous cytological identity, and revealed cryptic species, designated A and B, within S. tenebrosumTakaoka, Srisuka & Atiporn. A probable new species of microsporidium was discovered in the larval fat body of S. kiewmaepanense, suggesting that at least some symbiotic organisms of endemic hosts are also restricted to Doi Inthanon. A mitochondrial DNA analysis did not distinguish the two cryptic species of S. tenebrosum despite complete reproductive isolation chromosomally inferred from an absence of hybrids, emphasizing the need for integrated approaches to species problems.The chromosomes of all four analyzed species were monomorphic, or nearly so, perhaps reflecting the suppression of polymorphic inversions that otherwise would restrict recombination needed to generate adequate variation in the peripheral environment of the mountain summit.

Phylogenetic trees are crucial to many aspects of taxonomic and comparative biology. Many researchers have adopted Bayesian methods to estimate their phylogenetic trees. In this family of methods, a model of morphological evolution is assumed to have generated the data observed by the researcher. These models make a variety of assumptions about the evolution of morphological characters, and these assumptions are translated into mathematics as parameters. The incorporation of prior distributions further allows researchers to quantify their prior beliefs about the value any one parameter can take. How to translate biological knowledge into mathematical language is difficult, and can be confusing to many biologists. This review aims to help systematics researchers understand the biological meaning of common models and assumptions. Using examples from the insect fossil record, I will demonstrate empirically what assumptions mean in concrete terms, and discuss how researchers can use and understand Bayesian methods for phylogenetic estimation.