Who’s parasitizing tropical zooplankton? A survey of Cladocerans and their microparasites from the bays of Barro Colorado Island

Background/Question/Methods

Tropical/temperate comparisons are valuable for assessing basic patterns of ecological communities. Perhaps the most prominent pattern that unites tropical ecosystems is their unrivaled levels of biodiversity. This heightened biodiversity is thought to translate into greater enemy pressure, with tropical species encountering a broader array of predators, competitors, and parasites compared with their temperate counterparts. While competition and predation have been heavily investigated in tropical ecosystems, parasite pressure has not yet been fully incorporated into tropical/temperate comparisons. 

             One system that is promising for such a comparison is that of the zooplankton community and its species’ microparasites. Zooplanktonic hosts are abundant, easy to collect, and their parasites are easy to observe. Myriad studies have documented the diverse array of fungi, bacteria, and microsporidia infecting temperate freshwater zooplankters, but little complimentary work has been performed in tropical lacustrine ecosystems. We present the results of a preliminary investigation to characterize the diversity and abundance of zooplankton microparasites in Lake Gatún, Panama. Zooplankton were collected via vertical tow from three bays surrounding Barro Colorado Island across four time periods in spring 2015. Sampling was focused specifically on the three numerically dominant Cladoceran hosts, which were isolated and carefully assessed for signs of early- and late-stage infections. 

Results/Conclusions

We detected seven microparasites in our target Cladoceran hosts (Bosmina, Bosminopsis, Ceriodaphnia), with prevalences varying between 1% and 25% depending on the morphotype. Similar to many microparasites of temperate zooplankton, six of the seven microparasites we observed exhibit high pathogenicity, typically killing their hosts shortly after infection becomes detectable. These microparasites also appear to exhibit high host specificity, with only one of the seven infections appearing in more than one host species. Of particular interest is the cumulative pressure these parasites appear to be exerting on their host populations: results of this survey suggest that at least one fifth of each host population is infected by one of the observed microparasites.