Breeding systems in the clam shrimp family Limnadiidae (Branchiopoda, Spinicaudata)

Abstract

Abstract. Crustaceans in the class Branchiopoda exhibit a wide range of breeding systems, including dioecy (gonochorism), androdioecy, parthenogenesis, cyclic parthenogenesis, and hermaphroditism. The largest subgroup of the Branchiopods, the Diplostraca, is reported to encompass all five of these breeding systems. However, many of these reports are based primarily on simple observations of sex ratios in natural populations. Herein we report the beginnings of a more rigorous approach to breeding system determination in the Diplostraca, starting with the family Limnadiidae. We combine measurements of sex ratio, offspring rearings, and behavior to identify three breeding systems within the Limnadiidae: dioecy, androdioecy, and selfing hermaphroditism. To date, no instances of parthenogenetic reproduction have been identified in this family. Comparisons of breeding system determination via simple population sex ratios with our more controlled studies show that simple sex ratios can be useful when these sex ratios are ∼50% males (=dioecy) or 5–30% males (androdioecy). However, population sex ratios of 0–5% males or 35–45% males necessitate further investigation because estimates in these ranges cannot distinguish selfing hermaphroditism from androdioecy or androdioecy from dioecy, respectively. We conclude by noting that the genetic sex‐determining system outlined for one of these limnadiid species, Eulimnadia texana, provides a parsimonious framework to describe the evolution of the three breeding systems observed within the Limnadiidae.

Does life in unstable environments favour facultative selfing? A case study in the freshwater snail Drepanotrema depressissimum (Basommatophora: Planorbidae)

“…We are therefore still short of confirmed mixed-mating species in snails, and perhaps among hermaphroditic animals in general. The exceptions might be species exhibiting sexual polymorphisms such as the androdioecious freshwater shrimp Eulimnadia texana (Weeks et al 2008). More studies are required to substantiate this claim.…”

High lability of sexual system over 250 million years of evolution in morphologically conservative tadpole shrimps

“…In view of the sample sizes available to us we decided to conservatively categorise STUs into two sexual systems, gonochoric and androdioecious. In the AD notostracan species T. newberryi male proportions never exceed 27% [32,48] and in populations of AD Eulimnadia male proportions were always significantly lower than 50% male with a mode of ~20% [108]. Weeks et al [108] did, however, note that upper values for population sex ratio of AD taxa overlapped with the lower values of gonochoric taxa in the 35% - 45% range.…”

“…In the AD notostracan species T. newberryi male proportions never exceed 27% [32,48] and in populations of AD Eulimnadia male proportions were always significantly lower than 50% male with a mode of ~20% [108]. Weeks et al [108] did, however, note that upper values for population sex ratio of AD taxa overlapped with the lower values of gonochoric taxa in the 35% - 45% range. We therefore used a conservative population sex ratio cut-off of 30% male to assign an AD sexual system in the absence of additional histological or reproduction in isolation data in order to prevent misclassification due to stochastic variation in natural population sex ratios [51,109].…”

No amicable divorce? Challenging the notion that sexual antagonism drives sex chromosome evolution

“…Gynodioecy occurs in cnidarians [82][83][84] but is unknown in triploblastic animals. Androdioecy is slightly more common, occurring in branchiopod crustaceans [85], rhabditid nematodes [86] and a single vertebrate species, the mangrove killifish [87], but these androdioecious species appear to have evolved from dioecious ancestors rather than from hermaphrodites [88]. Androdioecy also occurs in barnacles where it is unclear whether it evolved from hermaphroditism or from dioecy [89].…”