Production of intersexes and the evolution of androdioecy in the clam shrimp Eulimnadia texana (Crustacea,Branchiopoda, Spinicaudata) |
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Authors: | STEPHEN C WEEKS SADIE K REED MICHELE CESARI FRANCA SCANABISSI |
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Institution: | 1. Department of Biology, Program in Evolution, Ecology, and Organismal Biology, ASEC 185 , University of Akron , Akron, OH, 44325-3908, USA Phone: +1 (330) 972-7155 Fax: +1 (330) 972-7155 E-mail: scw@uakron.edu;2. Dipartimento di Biologia Evoluzionistica Sperimentale , Università di Bologna , via Selmi 3, Bologna, 40126, Italy |
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Abstract: | Summary The production of low numbers of offspring that exhibit a mixture of male and female traits (termed “intersexes”) is commonly reported for crustaceans. The production of intersexes has been ascribed to both genetic and non-genetic (e.g., parasitic infections and environmental pollutants) causes. Herein we report on two observed types of intersexes in the clam shrimp Eulimnadia texana: (1) a “morphological” intersex, possessing secondary male characteristics (e.g., claspers) and an eggproducing gonad, and (2) a “gonadal” intersex, possessing primarily male traits (e.g., male secondary sexual characters and male gamete production) but also producing low levels of abortive female gametes. We propose that these intersexes are likely the products of low frequencies of crossing over between the sex determining chromosomes that result in the array of observed mixed sexual phenotypes. Additionally, we suggest that the low-level production of intersexes, combined with the ephemeral nature of the habitats occupied by these shrimp, may explain the preponderance of androdioecy (mixtures of males and hermaphrodites) found in these clam shrimp, and possibly branchiopods more generally. |
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Keywords: | Evolution of mating systems conchostraca gynandromorphs hermaphrodites sex determination crossing over |
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