Spatial and temporal variation in recruitment and its effects on regulation of parasite populations

Facilitating the recovery of insect communities in restored streams by increasing oviposition habitat

Recruitment limitation is known to influence species abundances and distributions. Recognition of how and why it occurs both in natural and in designed environments could improve restoration. Aquatic insects, for instance, rarely reestablish in restored streams to levels comparable to reference streams even years after restoration. We experimentally increased oviposition habitat in five out of 10 restored streams in western North Carolina to test whether insect egg-laying habitat was limiting insect populations in restored streams. A main goal was to test whether adding oviposition habitat in the form of rocks that partially protrude above the water surface could be used to increase the abundance and richness of stream insect eggs and larval insects in restored streams. Adding egg-laying habitat enhanced several response variables (e.g., protruding rocks, number of eggs, egg masses, egg morphotype richness, and oviposition habitat stability) to levels similar to those found in reference streams. Following the addition of protruding rocks, egg mass abundance increased by 186% and richness by 77% in restored-treated streams. Densities of larval insects that attached their eggs to protruding rocks showed an overall pattern consistent with treatment effects due to the combination of nonsignificant and significant increases of several taxa and not just one taxon. Our results indicate that these stream insect populations are limited by oviposition habitat and that adding egg-laying habitat alleviated this component of recruitment limitation. However, the weaker larval response indicates that additional post-recruitment factors, such as egg or larval mortality, may still be limiting a full recovery of larval insect abundances in these restored streams. This study shows the importance of integrating information from animal life histories, ecology, and geomorphology into restoration practices to improve the recovery of aquatic insects, which are commonly used to assess water quality and the biological efficacy of stream restoration.

HOST SPECIFICITY AMONG UNIONICOLA SPP. (ACARI: UNIONICOLIDAE) PARASITIZING FRESHWATER MUSSELS

Water mites of Unionicola spp. are common parasites of freshwater mussels as adults, living on the gills, or mantle and foot of their hosts and using these tissues as sites of oviposition. The present study addresses specialization among North American Unionicola mussel-mites using 2 measures of host specificity: (1) the number of host species used by a species of mite; and (2) a measure that considers the taxonomic distinctness of the hosts utilized by mites, weighted for their prevalence in the different hosts. Results of this study indicate the Unionicola spp. mussel-mites are highly host specific, with most species occurring in association with 1 or 2 species of hosts. If 2 or more host species are utilized, they are typically members of the same genus. These data are consistent with studies examining the dispersal abilities and host recognition behavior for members of the group. When the average values of host specificity for Unionicola subgenera were mapped on a phylogenetic tree for these taxa, a clade comprised of gill mites appeared to be more host specific than a clade consisting of mantle mites. There were, however, no apparent patterns of host specificity within each of the clades. Differences in specificity between the 2 lineages may reflect either a long evolutionary history that gill mites have had with host mussels or the intense competition among gill mites for oviposition sites within unionid mussels, leading to increased host specialization.