A conflict of morphological and genetic patterns in the Australian anostracan Branchinella longirostris

Abstract

Branchinella longirostris is a fairy shrimp endemic to ephemeral pools on granite outcrops in southwestern Australia. The patchy nature of its habitat is thought to result in a high degree of subdivision among populations, potentially promoting speciation. We combined traditional taxonomy with a molecular phylogeny of cytochrome c oxidase I (COI) to test whether B. longirostris could be a species complex and whether the frontal appendage on the second antennae of males is a suitable character to differentiate new species. We also used nested clade analysis to assess the population structure and demographic factors explaining the geographical distributions of the mt DNA haplotypes. The results show that shapes of frontal appendages are not congruent with the mitochondrial genetic structure; however, they are positively correlated with geography. We conclude that the frontal appendage in B. longirostris is either subject to selection or a result of morphological plasticity; thus, its use in taxonomy remains uncertain. The intraspecific divergence in B. longirostris (B7.7%) was approximately one third as large as the divergence from the outgroup (17.8-20.8%) and well within the ranges of divergence found in other crustaceans with fragmented population structure. There is some association between genetic structure and geography, resulting in the inference of restricted gene flow with isolation by distance and allopatric fragmentation as the most suitable models of the historical population processes. It is likely that the current distribution of haplotypes resulted from the dispersal of resting eggs by stochastic events (wind, birds) rather than from a fragmentation of previously continuous habitat as the estimated evolutionary age of the species (B6.1 my) is much younger than its habitat (50-100 my). We found some evidence on the genetic level to support the hypothesis that B. longirostris could be a complex of species; however, the lack of correlation between the genetic pattern and the reproductively important frontal appendage lends a support to a view that B. longirostris is a single species with an exceptionally high intraspecific diversity.

Overlooked cryptic endemism in copepods: Systematics and natural history of the calanoid subgenus Occidodiaptomus Borutzky 1991 (Copepoda, Calanoida, Diaptomidae)

“…Taylor et al, 1996;Braga et al, 1999;Korn et al, 2006;Thum and Harrison, 2009;Zofkova and Timms, 2009;Ketmaier et al, 2012), the application of standard molecular evolutionary rates to freshwater microcrustaceans is to be used with caution, as it might overestimate the divergence times of the studied taxa. This is possibly due to the very short life span, fast generation time and peculiar life history of microcrustacean species, which might give many more chances to mutations to take place, Table S1 for site details).…”

“…Knowlton and Weigt, 1998;Ketmaier et al, 2003). Furthermore, the possibility that mutagenic effects might act more incisively in shallow and ecologically-variable habitats has also to be considered: Zofkova and Timms (2009) suggested that the mutagenic effect of high UV exposure accelerates rates of molecular evolution in a fairy shrimp inhabiting shallow temporary ponds.…”

A revised identification guide to the fairy shrimps (Crustacea: Anostraca: Anostracina) of Australia

“…The species known from Australia are listed below, together with their presently known distribution and habitat preferences. The validity of most has been confirmed by molecular analysis (Pinceel et al, 2013b (Note that the frontal appendage (i) shows increasing size and complexity within set patterns with age and (ii) shows some variation in structure between populations (Geddes, 1981;Zofkova and Timms, 2009). …”

“…Species in the genus Branchinella have been subjected to molecular studies (Zofkova and Timms, 2009;Pincel et al 2013a). For almost all species morphological differences are supported by differences in their DNA, though in the variable and isolated populations of B. longrostris on Western Australian inselbergs the structure of the frontal appendage is not aligned with their cytochrome c oxidase I differences.…”

New challenges in anostracan research: old issues, new perspectives and hot topics

“…in Gandolfi et al, 2015; Branchinecta ferox (Milne-Edwards, 1840) in Rodríguez-Flores et al, 2017, but see also Aguilar et al, 2017 for a plea for caution when attributing species rank to divergent clades) to a pronounced morphological diversity not paralleled by an analogous molecular diversification (which is suggestive of phenomena of morphological plasticity, e.g., Zofkova & Timms, 2009).…”