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Complex worker caste systems have contributed to the evolutionary success of advanced ant societies; however, little is known about the developmental processes underlying their origin and evolution. We combined hormonal manipulation, gene expression, and phylogenetic analyses with field observations to understand how novel worker subcastes evolve. We uncovered an ancestral developmental potential to produce a "supersoldier" subcaste that has been actualized at least two times independently in the hyperdiverse ant genus Pheidole. This potential has been retained and can be environmentally induced throughout the genus. Therefore, the retention and induction of this potential have facilitated the parallel evolution of supersoldiers through a process known as genetic accommodation. The recurrent induction of ancestral developmental potential may facilitate the adaptive and parallel evolution of phenotypes.

abstract:The origin and divergence of the three living orders of amphibians (Anura, Caudata, Gymnophiona) and their main lineages are one of the most hotly debated topics in vertebrate evolution. Here, we present a robust molecular phylogeny based on the nuclear RAG1 gene as well as results from a variety of alternative independent molecular clock calibrations. Our analyses suggest that the origin and early divergence of the three living amphibian orders dates back to the Palaeozoic or early Mesozoic, before the breakup of Pangaea, and soon after the divergence from lobe-finned fishes. The resulting new biogeographic scenario, age estimate, and the inferred rapid divergence of the three lissamphibian orders may account for the lack of fossils that represent plausible ancestors or immediate sister taxa of all three orders and the heretofore paradoxical distribution of some amphibian fossil taxa. Furthermore, the ancient and rapid radiation of the three lissamphibian orders likely explains why branch lengths connecting their early nodes are particularly short, thus rendering phylogenetic inference of implicated relationships especially difficult.* E-mail: diegos@mncn.csic.es. † E-mail: vences@science.uva.nl. ‡ E-mail: marina@mncn.csic.es. § E-mail: rafaz@mncn.csic.es. Keywords: amphibian evolution, Pangaea breakup, molecular phylogeny, molecular clock, multiple calibrations, RAG1.Living amphibians (Lissamphibia) are a successful and highly diversified group of vertebrates that includes thousands of forms (5,770 species; AmphibiaWeb, January 26, 2005; http://www.amphibiaweb.org/) distributed throughout most habitats in all continents except Antarctica (Duellman and Trueb 1994). They experienced a long evolutionary history dating back at least to the early Triassic, the earliest known fossils being Triadobatrachus from Madagascar (Rage and Rocek 1989) and Czatkobatrachus from Poland (Evans and Borsuk-Bialynicka 1998). The Lissamphibia are widely thought to be a monophyletic group, constituted by three monophyletic orders (Anura, Caudata, and Gymnophiona) whose origin and interrelationships remain hotly debated (see Meyer and Zardoya 2003 for a recent review). The poor fossil record of some major lissamphibian groups and the fact that the three living amphibian orders possibly acquired their specialized morphology very early in their evolutionary histories (Zardoya and Meyer 2001) have left many questions unresolved regarding the origins, relationships, and historical distribution of the Lissamphibia.A recent molecular phylogeny of lissamphibians based on mitochondrial rRNA genes grouped salamanders and caecilians to the exclusion of frogs and suggested that the early evolutionary history of living amphibians was associated with the Mesozoic continental fragmentation of the supercontinent Pangaea (Feller and Hedges 1998). Paradoxically, some distributional patterns and some data from the fossil record (Estes and Wake 1972;Estes and Reig 1973;Rage and Rocek 1989;Jenkins and Walsh 1993;Duellman and Trueb 1994;Evans et ...

Most reported examples of change in vertebrate mitochondrial (mt) gene order could be explained by a tandem duplication followed by random loss of redundant genes (tandem duplication-random loss [TDRL] model). Under this model of evolution, independent loss of genes arising from a single duplication in an ancestral species are predicted, and remnant pseudogenes expected, intermediate states that may remain in rearranged genomes. However, evidence for this is rare and largely scattered across vertebrate lineages. Here, we report new derived mt gene orders in the vertebrate "WANCY" region of four closely related caecilian amphibians. The novel arrangements found in this genomic region (one of them is convergent with the derived arrangement of marsupials), presence of pseudogenes, and positions of intergenic spacers fully satisfy predictions from the TDRL model. Our results, together with comparative data for the available vertebrate complete mt genomes, provide further evidence that the WANCY genomic region is a hotspot for gene order rearrangements and support the view that TDRL is the dominant mechanism of gene order rearrangement in vertebrate mt genomes. Convergent gene rearrangements are not unlikely in hotspots of gene order rearrangement by TDRL.

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