Genetic relationships of the marine invasive crab parasite Loxothylacus panopaei: an analysis of DNA sequence variation, host specificity, and distributional range

Abstract

Host specificity is a key variable of the niche breath of parasites that can be an important determinant of a parasite's ability to invade new areas. There is increasing evidence that many parasite species may comprise a variety of genetically variable lineages, which differ in host specificity and geographic range. In this study, we (1) explored the extent of diversity in the invasive parasitic barnacle Loxothylacus panopaei (Rhizocephala) infecting mud crabs (2) examined the geographic origin for the invasive lineage and (3) assessed if further southward spread of the parasite may be impeded. Along the US Atlantic coast, L. panopaei infects different hosts in its invaded range (Chesapeake Bay to north of Cape Canaveral) compared to one portion of the native range in Southeast Florida. This difference was reflected in genetic lineages on two independent loci, mitochondrial cytochrome oxidase I and nuclear cytochrome c. Both loci were concordant in that they showed one lineage infecting crabs of the genus Panopeus in the native range and one lineage infecting Eurypanopeus depressus and Rhithropanopeus harrisii hosts in the invaded range and in the Gulf of Mexico, thus indicating Gulf of Mexico populations as the most likely source of introduction into Chesapeake Bay. Interestingly, the nuclear marker resolved an additional lineage of parasites infecting panopeid hosts in the native range. All three parasite lineages were well supported, but a decision about species status must await further analyses. Since its introduction in the 1960s, the invasive L. panopaei lineage has expanded its range southward along the US Atlantic coast, now almost reaching the northern limit of native Panopeus-infecting lineages at Cape Canaveral, Florida. We hypothesized that parasite-free E. depressus in Southeast Florida, living in sympatry with infected panopeid populations, might be resistant to infection by the invasive lineage. Our infection experiments rejected this hypothesis, suggesting that any impediment to further southward range expansion might be expected from temperature regimes of the subtropical zoogeographic region south of Cape Canaveral.

Host and parasite thermal ecology jointly determine the effect of climate warming on epidemic dynamics

“…However, at the South Carolina site, current infection prevalence was higher, and simulated temperature increases resulted in less dramatic prevalence declines than in Georgia; notably, the parasite persisted under the 2°C warming scenario. Our model results corroborate regional-scale observations that suggest that the parasite is thermally limited at its southern range edge (14).…”

“…We test the prediction that parasite and host traits have different thermal performance curves and quantitatively evaluate how differences in thermal performance affect predictions of climate warming on disease dynamics. We focus on an ectothermic host-parasite system that exhibits pronounced seasonal variation in infection prevalence (13) and whose biogeographic spread might be limited by high summer temperatures (14). Eurypanopeus depressus is an abundant oyster reef-dwelling crab that is infected with a nonnative rhizocephalan parasite, Loxothylacus panopaei.…”

Two new cryptic and sympatric species of the king crab parasiteBriarosaccus(Cirripedia: Rhizocephala) in the North Pacific

“…They observed maximal variations under 1% for each of the species, and a much larger genetic differences between them, ranging from 30 to 45%. Kruse, Hare & Hines ( 2012 ) reported a more complicated genetic relationship for the rhizocephalan Loxothylacus panopaei (Gissler, 1884) on different hosts from the US East Coast. Also in this study the host association was largely responsible for genetic variations.…”

Adaptation in marine invasion: a genetic perspective

“…Molecular tools often reveal that apparently widespread invasive species are instead cryptic species complexes, where genetic lineage may be correlated with environmental conditions (Bastrop et al 1998;FolinoRorem et al 2009;Mackie et al 2012). In an example of adaptation to a biotic agent, genetic studies strongly suggest that the parasitic castrating barnacle Loxothylacus panopaei is in fact a species complex with lineage-specific infection of its mud crab hosts (Kruse and Hare 2007;Kruse et al 2011). Comparisons of congeneric native and invasive species across several taxa have shown that the invaders often demonstrate higher tolerance of stresses than their native counterparts (Lenz et al 2011;Sorte et al 2011).…”

“…One shortcoming of many such studies is that it may be difficult to determine if these differences are truly heritable, or are the result of developmental or acclimatory plasticity (West-Eberhard 2003). In the case of some marine invasions, there is also the possibility that putatively population-level differences may instead be due to differences between uncharacterized cryptic species (Kruse et al 2011;Mackie et al 2012). In addition, experimental measures of differentiation may not have the resolution to detect subtle differences between populations, or may not measure the particular trait on which selection is acting.…”