Distinguishing North American D. pulex and D. pulicaria
North American D. pulex and D. pulicaria are thought to
have recently diverged from a common ancestor and adapted to distinct
environments while still experiencing introgression (Omilian and Lynch
2009; Cristescu et al. 2012). Such introgression may cause the D.
pulex /pulicaria hybrids to have mtDNA from either D.
pulex or D. pulicaria , thus biasing inferences based on trees
when derived from mtDNA data (Marková et al. 2013). Although the
nuclear-encoded lactate dehydrogenase locus (Ldh) has been used to
discriminate D. pulex and D. pulicaria , and was useful in
determining the species of NZ Daphnia samples, inferring species
solely based on the Ldh locus can still be misinformative due to
hybridization and backcrossing (Xu et al. 2013). For example, an Ldh SSDaphnia that derived from crossing between SF D.
pulex/pulicaria and SS D. pulex may be erroneously inferred as a
non-hybrid clone. To eliminate the limitations of a single nuclear
marker to derive inferences, we generated a set of 24,185 D.
pulicaria -specific nuclear markers that are monomorphic in every
non-hybrid D. pulicaria, and unique with respect to North
American D. pulex . These markers will be useful for diagnostic
purposes in other future studies involving these two species, including
the identification of hybrids. They may also serve as a resource for
studying genes involved in potential adaptive divergence betweenD. pulex and D. pulicaria.