Are mimics monophyletic? The necessity of phylogenetic hypothesis tests in character evolution

Abstract

BackgroundThe processes governing the origin and maintenance of mimetic phenotypes can only be understood in a phylogenetic framework. Phylogenetic estimates of evolutionary relationships can provide a context for analyses of character evolution; however, when phylogenetic estimates conflict, rigorous analyses of alternative evolutionary histories are necessary to determine the likelihood of a specific history giving rise to the observed pattern of diversity. The polyphenic butterfly Limenitis arthemis provides a case in point. This species is comprised of three lineages, two of which are mimetic and one of which is non-mimetic. Conflicting estimates of the relationships among these three lineages requires direct evaluation of the alternative hypotheses of mimicry evolution.ResultsUsing a coalescent framework, we found support for a sister-taxon relationship between the non-mimetic L. a. arthemis and the mimetic L. a. astyanax, congruent with the previous hypothesis that the non-mimetic form of L. a. arthemis was derived from a mimetic ancestor. We found no support for a mimetic clade (L. a. astyanax + L. a. arizonensis) despite analyzing numerous models of population structure.ConclusionsThese results provide the foundation for future studies of mimicry, which should integrate phylogenetic and developmental analyses of wing pattern formation. We propose future analyses of character evolution accommodate conflicting phylogenetic estimates by explicitly testing alternative evolutionary hypotheses.

Young relicts and old relicts: a novel palaeoendemic vertebrate from the Australian Central Uplands

“…This lineage diverged from extant relatives well before the major expansion of Australia's vast sandy deserts through the Plio-Pleistocene [2,5,56], but on a timeframe that is consistent with isolation by an earlier period of intensifying aridity in the late Miocene [16]. While the pattern shown by this taxon is currently unique, phylogenetic and distributional data suggest that a number of other relatively restricted and specialized saxicoline lizard taxa in the Central Uplands also show Miocene divergences and/or a lack of close relatives [13,42]. Thus, while a majority of Central Uplands relicts probably do postdate the Pliocene wet phase, as dated molecular phylogenies accumulate, it seems likely that a smaller number will be shown to have longer histories of isolation (especially in specialized taxa, those with low mobility and/or a high capacity to persist in localized microrefugia, e.g.…”

“…Thus, while a majority of Central Uplands relicts probably do postdate the Pliocene wet phase, as dated molecular phylogenies accumulate, it seems likely that a smaller number will be shown to have longer histories of isolation (especially in specialized taxa, those with low mobility and/or a high capacity to persist in localized microrefugia, e.g. [13,57]).…”

“…Thus the relative contribution of periods of aridification before and after the early Pliocene to shaping patterns of relictual endemism in the Central Uplands, other arid zone refugia in Australia, and elsewhere in the Southern Hemisphere, remains to be systematically addressed. However, molecular phylogenetic analyses of other Australia arid zone taxa, including other diplodactylid gecko genera with Gondwanan affinities [13,65], subterranean diving beetles [66] and salt lake beetles [7] are increasingly suggesting that the initial isolation of at least some arid zone relicts predates the Pliocene, and was potentially concurrent with widespread aridification during the Miocene. Many taxa showing long persistence tend to be ecologically specialized (e.g.…”

“…For all dating analyses, we used the Yule speciation prior (appropriate and widely used for relatively divergent lineages). Owing to potential issues when combining saturated mitochondrial data with deep calibrations (even after third codons have been removed) [13,30], we undertook dating analyses on both the combined dataset with third codons removed, and the nuclear alignment alone. For each data alignment, we also ran both uncorrelated-lognormal and strict clock models and compared model likelihoods by comparing AICM values as implemented in Tracer v. 1.6 [31].…”

“…Phylogenetic investigation of putative relict taxa endemic to ranges in arid Australia provides opportunities to understand how and when major environmental changes shaped biotic turnover across central Australia, and also assess what factors may have predisposed lineages to long persistence [11,13–15]. Recent palaeo-climatic analyses have provided compelling evidence that the overall trajectory towards increasing aridity across the Southern Hemisphere (and especially Australia) since the Late Miocene was punctuated by a sustained warm mesic interval during the early Pliocene [16].…”