Morphological disparity in populations with and without sexual reproduction: a case study in Eucypris virens (Crustacea: Ostracoda) ANGEL BALTANÁS 1 *, PALOMA ALCORLO 1 and DAN L. DANIELOPOL 2 1 Department of Ecology, Universidad Autónoma de Madrid, E-28049 Madrid, Spain 2 Institute of Limnology, Austrian Academy of Sciences, A-5310 Mondsee, Austria Received 1 May 2001; accepted for publication 7 September 2001 Morphological disparity in carapace outline was investigated in sexual and asexual populations of a widely spread nonmarine ostracod, Eucypris virens (Jurine, 1820) (Crustacea, Ostracoda). Only shape similarities have been con- sidered; size effect was removed by standardizing all outlines. Multivariate analysis of morphometric descriptors (Elliptic Fourier coefficients) show that efficient discriminant functions can be obtained to differentiate between sexual and asexual populations, left and right valves, as well as among local populations (86.7% correct classifica- tions in average). Principal component analysis revealed main patterns in shape variability among average popu- lation shapes. Sexual dimorphism is shown in body size but not in carapace outline. Although two morphotypes, unrelated to geographical locality, have been recognized, shape variation was largely continuous among all popu- lations. Disparity at the within-population level was similar for both right and left valves. Morphological disparity was lower in syngamic populations than in parthenogenetic populations. The results are discussed with regard to theories relating genetic and morphological diversity and to evidence on evolutionary ecology of reproductive modes in nonmarine ostracods. Advantages and further applications of morphometric analysis to taxonomic groups with rich fossil record, such as ostracods, is emphasized. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 75, 9–19. ADDITIONAL KEYWORDS: morphometrics – outline analysis – shape. Biological Journal of the Linnean Society, 2002, 75, 9–19. With 4 figures INTRODUCTION Taxonomic richness is but one of the many faces of biological diversity. Morphological diversity (hereafter, morphological disparity) is another. By disparity we mean the overall morphological variety within a taxon (or a population), regardless of the rank of that taxon (Foote, 1993). Because both kinds of diversity do not necessarily correlate (Cherry et al., 1979; Foote, 1993), comparisons between them provide helpful in-sight into evolutionary and ecological processes. Issues such as adaptive radiations, community con- vergence, extinction selectivity, and morphospace occupation have been addressed through the study of disparity among and within taxa at different ranks (Foote, 1997). The main sources of intra- specific morphological variation are genetic factors, environmental factors, and their interactions. Given that reproductive mode (sexual vs. asexual) influences both the genetic structure in the population and the response to environmental effects, we expect disparity patterns to differ between parthenogenetic and syn- gamic populations. Sexual reproduction is considered to be essential for evolutionary success, a statement supported by the fact that few taxa reproduce only asexually. However, a plethora of taxa have reached a compromise between both reproductive modes (Mogie, 1992; Bell, 1982; Hughes, 1989). Shifting from sexual to asexual re- production implies losing meiosis and syngamy, a pro- cess with predictable effects at the molecular level. For example, genomes are expected to contain highly divergent allelic sequences caused by a recurring mutation without posterior recombination (Welch & Meselson, 2000; but see Butlin, 2000). Impact on phenotypic traits, however, is more difficult to predict because relationships between genetic diversity and morphological differentiation are not straightforward ©2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 75, 9–19 9 * Corresponding author. E-mail: angel.baltanas@uam.es Downloaded from https://academic.oup.com/biolinnean/article-abstract/75/1/9/2638735 by guest on 22 May 2020