The potential for hybridization in freshwater copepods

Abstract

The importance of hybridization and hybrid zones in pelagic systems is largely unknown, in part because planktonic species are generally assumed to be reproductively isolated. However, lakes in their entirety represent potential hybrid zones throughout which sympatric species may mate and hybridize. Recent field evidence for the existence of intermediate phenotypes together with behavioral observations of heterospecific matings suggest that hybridization may be much more common than previously thought in these systems. This study examines the potential for hybridization of two related copepod species, Diaptomus minutus and D. pygmaeus, that co-occur in lakes throughout the northeastern United States. Field and experimental laboratory data were collected to: (1) compare the spatial and temporal occurrence of these two congeners in a single lake; (2) quantify the extent to which mating errors occur insitu; (3) examine the species specific mating cues that potentially affect the probability of hybridization; and (4) determine the potential for gametic compatibility and hybrid viability of these two species. D. minutus and D. pygmaeus are spatially and temporally sympatric, and the timing of their reproductive activity can be coincident insitu. One-directional mating errors occur frequently in both the laboratory and the field (e.g., upto 70% of D.minutus females in situ may carry spermatophores from D.pygmaeus males). Very low but successful production of hybrids also occurs, demonstrating that their gametes are indeed compatible and their hybrids are sometimes viable. These results underscore the potential for hybridization to play a greater role in speciation and contribute more to phenotypic diversity in aquatic crustacean communities than previously shown.

The influence of contact chemical signals on mate recognition in an harpacticoid copepod

“…These results contrast with studies that have documented interspeci¢c matings between several freshwater copepod species (Maier 1995;Chen et al 1997). Within laboratory crosses males of both C. canadensis and Coullana sp.…”

Heterospecific mating and partial prezygotic reproductive isolation in the planktonic marine copepods Centropages typicus and Centropages hamatus

“…Owing to the broad biogeographic distributions and common cooccurrence of congeneric copepod species (e.g., Frost 1969;Mullin 1969;Goetze 2005), mate-seeking adults often encounter closely related heterospecifics in the water column, and the ability to discriminate heterospecific from conspecific potential mates is an important component of reproductive success for individual copepods. Although we may expect individuals to excel at selective mate-choice behavior, given its importance to fitness, laboratory experiments and field observations on planktonic copepods in freshwater environments often have found significant levels of heterospecific mating and hybridization between species (up to 70% of females in the field) (Chen et. al.…”

Copepoda

“…This involves the male attaching to copepodidstage females (as early as CI in some species) so that they maximize their chances of being able to mate with a virgin female [99] . Interspecific mating has been observed in some cyclopoid species [234] , and hybridization has been reported between two species of Leptodiaptomus [49] .…”