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The ability to detect predators at a distance through chemical cues is often essential for prey, but spatial variation in predator presence and species may promote variability in the reactions of prey subpopulations. We collected isopods (Caecidotea communis) from three ponds: two with fish (sunfish in one, shiners in the other), and one without. We exposed individuals from these three subpopulations to kairomones and diet cues released by sunfish (Lepomis spp.) or golden shiners (Notemigonus crysoleucas). We used time-lapse photography to calculate the rate of movement and proportion of time isopods spent moving, both soon after cue introduction and twenty-five minutes later. Thus, we tested for reactions to cues, for rapid cue degradation or short-term habituation, and for effects of natal pond. The isopods from all subpopulations did not alter their rate of movement nor their percent of time moving when exposed to dechlorinated tap water or cues from sunfish. The isopods from the pond containing shiners significantly increased their proportion of time moving, and showed a not significant tendency to move more rapidly, when exposed to cues from shiners as opposed to dechlorinated tap water. Our results are the first to demonstrate that isopods may lack a behavioral response to chemicals indicating likely imminent danger from the same species of fish as occur in their natal pond.

Riparian isopods possess many traits that make them ideal candidates for a wide range of ecological and evolutionary studies, but they are under-utilized because long-term maintenance under laboratory conditions has been largely unsuccessful. We explored a variety of experimental conditions to determine those necessary to maintain captive populations. Our studies demonstrated that starting colonies with water from the natal stream, filtering the water in a way that causes agitation at the surface of the water, maintaining colonies in full-spectrum light at room temperature or colder, lining the bottom of containers with a coarse benthos, and providing a leaf pack that contains Norway maple leaves are important criteria for successful maintenance of individuals of Lirceus sp. colonies for periods of over 6 weeks in the laboratory. Water changes do not require addition of water from the natal stream, whether the containers are glass or plastic is inconsequential, aeration does not need to be high-powered, and refrigeration of colonies is not necessary for this species of riparian isopod. We expect identifying the minimum husbandry needs will facilitate research using these organisms.

In dynamic environments such as the rocky marine intertidal zone, epibiosis may promote the survival of some organisms. We compared the species composition and prevalence of the epibiotic community on different species of molluscan shells to those on neighboring rock at three sites and two tidal heights per site on San Juan Island, Washington (48°N, 123°W; summer 2014). Across all three sites and both tidal heights examined, the algal species dominating the bedrock did not match the dominant epibiotic species. Most epibiotic species were from a subset of the less common bedrock species. Within the lower tidal height, many potential host shells lacked epibionts, but the bedrock was heavily colonized. Our findings suggest that shells do not represent a microhabitat that is more beneficial to settlers than the surrounding bedrock. Epibiosis is unlikely to elevate local species diversity in this ecosystem because the few epibionts were generally from a subset of the species on the bedrock. Smooth-shelled limpets had a significantly greater prevalence of epibiosis in the lower than in the higher tidal height, but the prevalence of epibiosis did not differ significantly between tidal heights for carnivorous, spired-shell species. This variation among basibionts in pattern of prevalence across tidal heights suggests that the carnivorous snails are more likely than the limpets to range across intertidal heights.

Individuals of the epibiotic gastropod Crepidula adunca predominantly utilize the gastropod Calliostoma ligatum as their hosts in the San Juan Islands, Washington, rather than exploiting other potential host species. Snails of Margarites pupillus would appear to be particularly good alternate hosts, given their similarities in microhabitat choice, shell shape, and taxonomic closeness with Calliostoma ligatum. However, M. pupillus are almost never utilized as a host by Crepidula adunca. We examined the reasons for host fidelity by Crepidula adunca in the San Juan Islands. The small but voracious sea star Leptasterias hexactis was common across all our intertidal survey sites and consumed significantly more M. pupillus than Calliostoma ligatum in laboratory experiments. Individuals of Calliostoma ligatum stimulated by tube feet from Leptasterias hexactis moved significantly more quickly than non-stimulated individuals, but snails of this species stimulated by Pycnopodia helianthoides did not move at a significantly different rate than non-stimulated snails. There was a significant positive correlation between gastropod size and the rate of movement for Calliostoma ligatum stimulated by Leptasterias hexactis, but this correlation was not significant for non-stimulated individuals. Neither stimulation by asteroids nor gastropod size (whether for stimulated or non-stimulated snails) had a significant effect on the rate of movement for M. pupillus. Thus Calliostoma ligatum, and especially large individuals of this species, react more than M. pupillus to the presence of a common predator (Leptasterias hexactis) in such a way that likely elevates the snails' chance of escape. Finally, we found that Calliostoma ligatum used both chemical and physical defenses to effectively repel attacks by Leptasterias hexactis, while defenses by M. pupillus were less successful. We suggest that epibiotic Crepidula adunca specialize on Calliostoma ligatum in the San Juan Islands because this particular host species is more likely to protect the epibiont from shared doom due to its effective defenses against potential predators.

Understanding of the conditions encouraging the evolution of kleptoparasitism has been limited by the preponderance of attention focused on a limited number of taxa (predominantly birds). However, most animal taxa contain kleptoparasitic members. In many ways, adult birds are aberrant because most are acrobatic, capable of three-dimensional movement, and steal from hosts that are capable of similar feats. The mobility of kleptoparasites and their hosts falls along a continuum, with the acrobatic birds at one end and sessile hosts and kleptoparasites at the other. Considering sedentary systems requires amendments to the criteria previously outlined as necessary for kleptoparasitism. Kleptoparasitic interactions between agile participants are ephemeral, involve numerous hosts over the lifetime of the kleptoparasite, and usually rely on vision. Large concentrations of hosts and large, high-quality food items are important in mobile systems. By contrast, the long-term, intimate associations of sedentary interactions demand that the host not consume the kleptoparasite's offspring and that the host must either have a longer life cycle than the kleptoparasite or be located in aggregations that have staggered life cycles (so the kleptoparasite can move to a new host when the original host dies). Expanding studies of kleptoparasitism to other taxa will differentiate between the selective pressures and evolutionary responses that are universal among kleptoparasitic symbioses and those that are restricted to certain groups. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 93, 745–762.

The marine gastropod Trichotropis cancellata is a facultative kleptoparasite, either suspension feeding or parasitically stealing food from tube-dwelling polychaete worms. To determine whether conclusions drawn from long-term studies in the San Juan Islands, Washington, about the relative importance of suspension feeding and kleptoparasitism can be applied generally to T. cancellata across its biogeographic range, I expanded earlier studies to Alaska and British Columbia. Kleptoparasitism is pervasive throughout the range of T. cancellata, occurring with equal frequency throughout the areas studied. The average density and size of worm hosts are relatively constant across this range. Snail and worm densities are not significantly correlated at the larger scale of site (averaged over nearby sampling locations clustered around a city), but are correlated at the smaller local scale (within a sampling location). Larger worms do not support more snails. The abundance of uninfected worm hosts is usually not limiting, except potentially in some sampling locations in southwest Alaska where the use of a novel host (a holothurian) may be the result of low densities of uninfected worms. Additionally, I documented the feeding behaviours of other trichotropid species in these regions. Trichotropis conica is the second confirmed kleptoparasite within the genus Trichotropis, with kleptoparasitism as frequent in this species as in T. cancellata. Like T. cancellata, all sizes observed of T. conica are kleptoparasites. On the other hand, Trichotropis insignis is an obligate suspension feeder. Further studies are needed to determine exactly how many times this behaviour has arisen and been lost in Capulidae and related families.

Generalist parasites may disproportionately use certain hosts because of different benefits associated with each host species. I measured the growth rate of the marine snail Trichotropis cancellata, a facultative kleptoparasite that can suspension feed and steal food, on different hosts to determine the relative nutritional benefits of each host. The variation in tentacle (feeding structure) area among the hosts studied had the potential to provide parasitic snails with different amounts of nutrition for growth. In field experiments, suspension-feeding snails isolated from potential hosts grew at a similar rate to snails on brachiopods and significantly more slowly than snails on the following polychaete worms: Serpula columbiana (Serpulidae), Pseudopotamilla ocellata (Sabellidae), Schizobranchia insignis (Sabellidae), and Eudistylia vancouveri (Sabellidae). However, choice among worm hosts affected snail growth rates only in the fall, when phytoplankton levels are low. At this time, snails parasitizing the sabellids Schizobranchia and Eudistylia grew more quickly than snails on Serpula. In the spring and summer, with high levels of phytoplankton, Trichotropis grew at similar rates on all worm species tested. Trichotropis spent approximately the same time stealing food from each worm host species, >50% of the time the worms had their tentacles extended (the difference among hosts was not significant). This finding demonstrates that the similarity of snail growth rates on different worm species is not due to the snails compensating for poor hosts (worms that provide food at a slower rate) by spending more time stealing food. Snails in choice experiments preferred live Serpula to empty Serpula tubes, indicating that at least some of the cue(s) snails use to identify hosts are derived from living host tissues. In choice racks containing live Serpula and live Schizobranchia, snails did not choose one host worm significantly more often than the other. Because Trichotropis grows faster on sabellids than serpulids in the fall, I predicted that snails in nature would infect sabellids more often than other species. However, snails were usually distributed randomly among host species. In the few cases where the snails showed a significant preference among host species, proportionally more snails were found on serpulids than on sabellids or sabellarids. This study is the first to quantify under natural conditions the growth benefits of a kleptoparasite across the range of possible hosts, and implies that factors other than growth rate influence host choice specificity in the marine kleptoparasite T. cancellata.

Although theory pinpoints the reliability of cues as an important condition for the evo- lution of inducible defenses, the specificity of cues is poorly known in most systems. The bryozoan Membranipora membranacea produces long, energetically-costly spines in response to a trophically specialized nudibranch Doridella steinbergae, but the range of nudibranchs that trigger this response is unknown. We tested chemical cues from 14 nudibranch species from 4 suborders, the snail species Lacuna vincta, and an abiotic treatment (desiccation) for their ability to induce spines. Both corner spines (arising from the corners of the zoecium) and membranous spines (arising from the frontal membrane of the zooid) were observed. Of the nudibranch species tested, 57% induced corner spines in at least 1 trial: 4 predators of M. membranacea (Onchidoris muricata, Polycera zosterae, Triopha catalinae, and D. steinbergae) and 4 non-predators (Coryphella sp., Archidoris odhneri, Cadlina luteomarginata, and Dirona albolineata). Although many nudibranchs occasionally triggered spines, the spine response was most reliably and fully developed in response to the bryozoan's primary predator, D. steinbergae. All other species that induced corner spines, except Coryphella sp., failed to induce spines in all trials. Membranous spines were sometimes produced in response to D. stein- bergae, O. muricata, P. zosterae, A. odhneri, and Coryphella sp. The last 2 species are not known to prey on M. membranacea. Neither corner nor membranous spines were ever induced by Discodoris sandiegensis, Dendronotus frondosus, Dendronotus diversicolor, Tritonia festiva, Flabellina trilineata, Phidiana crassicornis, or desiccation. Of these non-inducers, only P. crassicornis feeds on M. mem- branacea, and this species typically causes little damage. There was no phylogenetic pattern among nudibranchs inducing spines. The production of corner and membranous spines were correlated. Corner spines appeared to have a lower induction threshold than membranous spines; the latter are therefore a more conservative indication of induction. Counter to the hypothesis of Adler & Grun- baum, the spine-inducing chemical cue(s) from D. steinbergae is probably not a mating pheromone, as D. steinbergae egg masses and pre-reproductive slugs induced spines. We conclude that M. mem- branacea often produces spines in response to predators that are deterred by spines, but seems surprisingly responsive to cues from some benign nudibranch species.

Individuals of the marine snail Trichotropis cancellata can either suspension feed or steal food from tube-dwelling polychaete worm hosts (kleptoparasitism). Because kleptoparasitism is facultative in this case, the performance of both members can be evaluated separately and together. I used field experiments to compare the growth of suspension feeding snails with that of snails (either singly or in groups) on Serpula columbiana polychaete hosts. All sizes of T. cancellata grew more quickly (up to 18 times faster) when parasitizing S. columbiana than when restricted to suspension feeding. Kleptoparasitism provided a proportionally greater growth benefit for small and medium- sized snails than for larger ones, suggesting that smaller gastropods are more food-limited when suspension feeding. Fecundity was positively correlated with snail size, so the growth benefits of kleptoparasitism are likely to be selectively advantageous. Increasing numbers of medium-sized snails on a host reduced individual snail growth rates, suggesting competition for the worm's food. All snails were equally affected; there was not a superior competitor among medium-sized snails. Para- sitism was experimentally demonstrated because serpulid worms grew their tubes more slowly when supporting parasitic snails and were increasingly negatively affected by additional medium-sized parasitic snails. Adding large parasitic snails did not exacerbate the negative impact on worm tube growth, so I concluded that a single large snail reduces worm hosts to their minimal rate of tube extension. Suspension feeding T. cancellata gain additional resources when they switch to klepto- parasitism.

Lecithotrophic echinoderm eggs and larvae are likely to possess deterrents to predation because they are large, lack behavioral defenses, and are often conspicuously colored. We performed laboratory feeding assays to test deterrence in multiple developmental stages of common shallow-water lecithotrophic asteroids and holothuroids in the San Juan Islands, Washington (seven asteroids, five holothuroids) to five functionally diverse, potentially sympatric predators (sculpins, shrimp, ascidians, and two species of anemones). At least one developmental stage of most echinoderm species tested deterred at least one predator (causing food rejection). Using sculpins as predators, the hypothesis that deterrence varied among developmental stages of a species was rejected for the four echinoderm species in which older embryos were tested. Different predator species often responded differently to the same developmental stage. Compared to the invertebrate predators, sculpins were usually the most sensitive assay predator. The present results provide additional support for the hypothesis that lecithotrophic eggs and larvae are deterrent, and in this study the deterrents persisted through early life stages. Because these stages lack obvious structural or behavioral defenses, the most likely source of their deterrence is chemical.

The sulfur butterflies, Colias spp., and their relatives in the family Pieridae have been the subjects of diverse behavioral, ecological, and evolutionary studies. However, their phylogeny is uncertain in many respects. We used DNA sequences from 2 mitochondrial gene blocks, 333 bp of the cytochrome oxidase I subunit (CO I) and 1,261 bp from the 2 ribosomal genes and the tRNA between them (rDNA), as character sources to test existing phylogenetic hypotheses and begin to infer others. The rDNA block resolves better at deeper nodes of the phylogeny, and the CO I block at shallower nodes. Our results support sister status for subfamilies Coliadinae and Pierinae within Pieridae; independent tribal status for Euchloini and Pierini within Pierinae; status as sister genera for Colias and Zerene within Coliadinae; and monophyly within subgenus C. (Eucolias) of all North American Colias studied. Our results suggest that the Neotropical coliad genus Eurema may warrant splitting, as some early workers proposed, but do not support the recently proposed splitting of Eurasian C. erate from subgenus C. (Eriocolias) into the separate subgenus C. (Neocolias) . (Lepidoptera: Pieridae)