DOI: 10.5061/dryad.fbg79cnt8
title: A novel body plan alters diversification of body shape and genitalia in live-bearing fish

description: Major evolutionary innovations can greatly influence subsequent evolution.
 While many major transitions occurred in the deep past, male live-bearing
 fishes (family Poeciliidae) more recently evolved a novel body plan. This
 group possesses a three-region axial skeleton, with one region—the
 ano-urogenital region—representing a unique body region accommodating male
 genitalic structures (gonopodial complex). Here we evaluate several
 hypotheses for the evolution of diversity in this region and examine its
 role in the evolution of male body shape. Examining Gambusia fishes, we
 tested a priori predictions for 1) joint influence of gonopodial-complex
 traits on mating performance, 2) correlated evolution of
 gonopodial-complex traits at macro- and microevolutionary scales, and 3)
 predator-driven evolution of gonopodial-complex traits in a
 post-Pleistocene radiation of Bahamas mosquitofish. We found the length of
 the sperm-transfer organ (gonopodium) and its placement along the body
 (gonopodial anterior transposition) jointly influenced mating success,
 with correlational selection favoring particular trait combinations.
 Despite these two traits functionally interacting during mating, we found
 no evidence for their correlated evolution at macro- or microevolutionary
 scales. In contrast, we did uncover correlated evolution of modified
 vertebral hemal spines (part of the novel body region) and gonopodial
 anterior transposition at both evolutionary scales, matching predictions
 of developmental connections between these components. Developmental
 linkages in the ano-urogenital region apparently play key roles in
 evolutionary trajectories, but multiple selective agents likely act on
 gonopodium length and cause less predictable evolution. Within Bahamas
 mosquitofish, evolution of hemal-spine morphology and gonopodial anterior
 transposition across predation regimes was quite predictable, with
 populations evolving under high predation risk showing more modified hemal
 spines with greater modifications and a more anteriorly positioned
 gonopodium. These changes in the ano-urogenital vertebral region have
 facilitated adaptive divergence in swimming abilities and body shape
 between predation regimes. Gonopodium surface area, but not length,
 evolved as predicted in Bahamas mosquitofish, consistent with a previously
 suggested tradeoff between natural and sexual selection on gonopodium
 size. These results provide insight into how restructured body plans offer
 novel evolutionary solutions. Here, a novel body region—originally evolved
 to aid sperm transfer—was apparently co-opted to alter whole-organism
 performance, facilitating phenotypic diversification.
description: Data for this study comprises several different types of
 datasets: 1. Laboratory mating experiment measuring the
 effects of two morphological traits on mating success.
 2. Comparative analysis of morphological trait evolution using
 phylogenetically indepedent contrasts (using separate phylogenies based on
 either nuclear and mitochondrial DNA). Measurements of traits from digital
 x-ray images. 3. Tests of morphological differentiation
 between predation regimes using wild-caught Bahamas mosquitofish from blue
 holes on Andros Island, The Bahamas (individual dataset and
 population-mean dataset). Measurements of traits from digital x-ray
 images. 4. Tests of genetic basis for morphological
 differentiation between populations using a laboratory common-garden
 experiment using Bahamas mosquitofish from 8 blue holes on Andros Island,
 The Bahamas. Measurements of traits from digital x-ray images.
description: Information for the datasets are provided in the first sheet of
 the Excel file.