The potential for hybridization in freshwater copepods

Area of Science:

• Ecology
• Evolutionary Biology
• Limnology

Background:

• Hybridization is poorly understood in pelagic systems, with planktonic species often assumed reproductively isolated.
• Lakes can function as hybrid zones, facilitating interspecies mating and hybridization among co-occurring species.
• Recent findings suggest hybridization may be more prevalent in aquatic systems than previously recognized.

Purpose of the Study:

• To investigate hybridization potential between two related copepod species, Diaptomus minutus and D. pygmaeus, in northeastern US lakes.
• To assess spatial-temporal overlap, mating errors, species-specific mating cues, gametic compatibility, and hybrid viability.
• To determine the role of hybridization in speciation and phenotypic diversity within aquatic crustacean communities.

Main Methods:

• Field surveys to compare spatial and temporal distribution of D. minutus and D. pygmaeus in a shared lake.
• Laboratory experiments to quantify mating errors and assess species-specific mating cues.
• Evaluation of gametic compatibility and hybrid offspring viability through controlled crosses.

Main Results:

• D. minutus and D. pygmaeus exhibit spatial and temporal sympatry, with overlapping reproductive periods.
• Frequent one-directional mating errors were observed in both field and laboratory settings, with up to 70% of D. minutus females carrying spermatophores from D. pygmaeus males.
• Successful, albeit low-frequency, hybrid production confirmed gametic compatibility and occasional hybrid viability.

Conclusions:

• Hybridization between D. minutus and D. pygmaeus is a demonstrated phenomenon in natural lake systems.
• Mating errors and successful hybridization challenge the notion of reproductive isolation in these planktonic copepods.
• Hybridization may play a significant role in the speciation process and contribute to phenotypic diversity in freshwater crustacean communities.