Conus miliaris

Abstract: First observations are reported of predator-prey relationships among gastropod mollusks of the depauperate, Indo-West Pacific derivative, intertidal and shallow subtidal benthic fauna of Easter Island. Conus miliaris, which will be reported in detail in a separate paper, and Pisania decapitata englerli prey on polychaete annelids; Mitraflavocingulatapreys on sipunculans; and Neothais nesiotes preys on barnacles intertidally and gastropods subtidally. Gastropods of at least three species are eaten by the most common Easter Island starfish, Astrostole paschae. EASTER ISLAND, THE MOST ISOLATED island in the Pacific Ocean, may be viewed as a natural experiment in the assembly of biotic communities (Diamond and May 1976). For this reason, its inshore marine biota has been studied increasingly in recent years; the primarily tropical Indo-West Pacific affinity and limitednumbef of species 6nhe fishes and invertebrates have drawn particular at­ tention (Devaney 1973, Fell 1974, Garth 1973, Kohn and Lloyd 1973, Randall 1976). However, the biological interactions of these animals have remained unstudied. In the course of an ecological study of the predatory gastropod Conus miliaris at Easter Island, I examined individuals of three co­ occurring predatory gastropod species for evidence of the nature of their prey, and I examined specimens of the starfish Astrostole paschae (Clark) to determine whether its diet includes gastropods. The results of the Conus study will be published separately; here, I report briefly on an initial effort to determine predator-prey relationships involving the other gastropods.

Abstract: Food and microhabitat resource use by vermivorous gastropods on Heron reef crest was analyzed from 3 samples, separated by 12 and 20 month periods. The assemblage is typical of those of other Indo-Pacific sites with respect to mean shell size and population density. These 2 parameters varied among samples for some species, although no general trends occurred. Fluctuations in species' size and density are assumed not to have significantly influenced availability of prey or microhabitat types.Colwell and Futuyma's (l971) method of ecological scaling of resource use data, was used for microhabitat niche breadth and overlap estimation, allowing between-sample comparisons. Data on gastropod activity in aquaria, together with microhabitat use patterns, demonstrated significant day-night differences in microhabitat resource use. Gastropods occurred mainly in the structurally complex, 'refuge' microhabitats during the day and showed an increased abundance in smooth, exposed, 'foraging' microhabitat at night compared with the day. Nassarius gaudiosus is the most extreme microhabitat specialist during the day and the most extreme microhabitat generalist at night. A similar, although less extreme trend was exhibited by other gastropods.Microhabitat #4 (sand under rocks) and #2 (sand in depressions) are the major contributors to structural heterogeneity in the gastropods' environment. Multiple regression analysis demonstrated a significant relationship between pooled gastropod abundance (= pooled abundance of N. gaudiosus, Vasum turbinellus, Conus miliaris, C. coronatus, C. flavidus) and the abundance of microhabitat #2. The abundances of N. gaudiosus, C. coronatus and C. flavidus each showed a significant relationship with the abundance of microhabitat #4. Therefore N. gaudiosus is influenced, directly or indirectly, by the availability of its chief refuge microhabitat. Since C. coronatus and C. flavidus occur mainly in microhabitat #2 during the day, the cause of the relationship between the abundance of microhabitat #4 and the abundance of these 2 species is unclear. The availability of the chief foraging microhabitat #7 (smooth limestone with a thin layer of algal-bound sand) does not limit gastropod abundance.Microhabitat niche overlap was high for C. coronatus, C. miliaris, C. flavidus, V. turbinellus and N. gaudiosus at night and was also high during the day for all these species, except N. gaudiosus. These data are consistent with Pianka's (1976) hypothesis that maximum tolerable niche overlap increases as resource availability increases.There were 8 gastropod species for which 5 or more diet records were obtained and two distinct feeding strategies are discernable within the gastropod assemblage. Members of the first group consume only errant polychaetes (mostly eunicids) and, in order of increasing food niche breadth, are Conus miles, C. miliaris, C. sponsalis, C. coronatus and N. gaudiosus. These species show a negative relationship between predator body size and food niche breadth, a result consistent with Leviten's (1976) model of Conus feeding strategies. Species of the second group consume sedentary polychaetes as part, or all of their diet and are Peristernia nassatula, C. flavidus and V. turbinellus, in order of increasing food niche breadth. For these species, predator body size and food niche breadth are positively related, which is consistent with Schoener's (1971) feeding strategy model. Because errant polychaetes were relatively more abundant in substratum samples than were sedentary worms, the observed dichotomy in feeding strategies of vermivorous gastropods probably results from the difference in availability of prey for the two groups. As the body size of gastropods that consume sedentary worms increases, relative prey availability is reduced and therefore food niche breadth increased. In contrast, the consumers of the very abundant errant polychaetes are not prey limited as gastropod body size increases, and the narrow food niche breadths of large-bodied Conus result from increasing minimum prey size. Data on abundance and spatial predictability of polychaetes, combined with the gastropod diet data, are consistent with the predictions of optimal foraging theory, that abundant food supplies will lead to selective foraging and narrow food niche breadths, particularly in the case of C. miles and C. miliaris which specialize on the very abundant eunicid worms and P. nassatuta which specializes on chaetopterids, the most abundant sedentary polychaetes.For Heron Reef vermivorous gastropods, the microhabitat data are consistent with the intermediate disturbance hypothesis of community structure maintenance (Connell, 1978), which assumes the assemblage is in a non-equilibrium state, and the food data are consistent with the niche diversification hypothesis (Connell, 1978), which assumes the assemblage is in an equilibrium state. This apparent paradox may result from multiple factors operating to organize communities at different spatial and temporal scales,

Abstract: Oceanic islands represent excellent systems for studying the link between geographic isolation and population divergence. Easter Island is the world’s most isolated island and exhibits a high level of endemicity in the nearshore marine environment. Yet few studies have examined the effect of such extreme isolation on the divergence of populations of widespread species that occur at Easter Island. Conus miliaris, a marine gastropod distributed throughout much of the Indo-West Pacific, occurs at Easter Island where the population is ecologically and morphologically distinct from other populations of the species. To determine whether these phenotypic differences are associated with genetic isolation of the Easter Island population, we investigated the phylogeography of this species by examining mitochondrial COI sequences obtained from 141 individuals from eight localities occurring predominantly in the western, central and southeastern Pacific. Results from our analyses show that C. miliaris at Easter Island differs genetically from other populations. We estimate that C. miliaris colonized Easter Island shortly after the origin of the island ≤0.7 million years ago and that since population founding, gene flow has occurred predominantly from Easter Island to the west and that little migration has occurred into Easter Island.

Abstract: Background: Ecological release is coupled with adaptive radiation and ecological diversification yet little is known about the molecular basis of phenotypic changes associated with this phenomenon. The venomous, predatory marine gastropod Conus miliaris has undergone ecological release and exhibits increased dietary breadth at Easter Island. Methodology/Principal Findings: We examined the extent of genetic differentiation of two genes expressed in the venom of C. miliaris among samples from Easter Island, American Samoa and Guam. The population from Easter Island exhibits unique frequencies of alleles that encode distinct peptides at both loci. Levels of divergence at these loci exceed observed levels of divergence observed at a mitochondrial gene region at Easter Island. Conclusions/Significance: Patterns of genetic variation at two genes expressed in the venom of this C. miliaris suggest that selection has operated at these genes and contributed to the divergence of venom composition at Easter Island. These results show that ecological release is associated with strong selection pressures that promote the evolution of new phenotypes.