Speciation in Daphnia

Abstract

The microcrustacean Daphnia is arguably one of the most studied zooplankton species, having a well understood ecology, life history, and a relatively well studied evolutionary history. Despite this wealth of knowledge, species boundaries within this genus often remain elusive and the major evolutionary forces driving the diversity of daphniids remain controversial. This genus contains more than 300 species with multiple cryptic species complexes, with many closely related species able to hybridize. Here we review speciation research in Daphnia within the framework of current speciation theory. We evaluate the role of geography, ecology, and biology in restricting gene flow and promoting diversification. Of the 253 speciation studies on Daphnia, the majority of studies examine geographic barriers (55%). While evidence shows that geographic barriers play a role in species divergence, ecological barriers are also likely prominent in Daphnia speciation. We assess the contribution of ecological and non-ecological reproductive isolating barriers between closely related species of Daphnia and found that none of the reproductive isolating barriers are capable of restricting gene flow completely. Research on reproductive isolating barriers has been disproportionally focused on two species complexes, Daphnia pulex and Daphnia longispina. Lastly, we identify areas of research that remain relatively unexplored and discuss future research directions that build our understanding of speciation in daphniids.

Variation in heat shock protein 40 kDa relates to divergence in thermotolerance among cryptic rotifer species

“…This acts as a pre-zygotic isolation mechanism by facilitating differences in timing of reproduction and population growth based on distinct environmental cues (i.e., temperature, photoperiod) and thus maintaining the species boundaries. Such pre-zygotic isolation by season has also been observed among Daphnia species (reviewed in 88 ). This mechanism may however be imperfect under certain environmental conditions, leading to occasional hybridization, as observed in our study.…”

Editorial 2022

“…Ephippia are resistant to desiccation and freezing, and can potentially hatch during decades or centuries when stored in sediments. Chin and Critescu (2021) examined speciation in the Daphnia genus, by evaluating the respective roles of geography, ecology, and biology in restricting gene flow and promoting diversification. Elasmobranchs (sharks and rays) have a very different breeding system than other fish. Their reproduction requires mating and internal fertilization, and females produce few large eggs.…”

The roles of recombination and selection in shaping genomic divergence in an incipient ecological species complex

“…The D . pulex species complex consists of a collection of morphologically similar, but ecologically distinct species (Colbourne et al, 1998; Crease et al, 2012), which includes species that have arisen from hybridization and polyploidization events (Chin & Cristescu, 2021; Dufresne & Hebert, 1997). Although many of the evolutionary relationships within the D .…”

“…Although many of the evolutionary relationships within the D . pulex group remain poorly resolved at the genomic level (Ye et al,2021), Daphnia pulex and Daphnia pulicaria are thought to represent a case of rapid ecological speciation (Chin & Cristescu, 2021; Pfrender et al, 2000). Specifically, D .…”