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Species distributions are shifting in response to increased habitat temperatures as a result of ongoing climate change. Understanding variation in physiological plasticity among species and populations is important for predicting these distribution shifts. Interspecific variation in intertidal ectotherms’ short-term thermal plasticity has been well established. However, intraspecific variation among populations from differing thermal habitats remains a question pertinent to understanding the effects of climate change on species’ ranges. In this study, we explored upper thermal tolerance limits and plasticity of those limits using a foot muscle metric and 2 cardiac metrics (Arrhenius breakpoint temperature, ABT, and flatline temperature, FLT) in adult file limpets Lottia limatula. Limpets were collected from thermally different coastal and inland-estuarine habitats and held for 2 wk at 13, 17 or 21°C prior to thermal performance assays. Compared to limpets from the warm estuary site, limpets from the cold outer coast site had similar foot muscle critical thermal maxima (CTmax; 35.2 vs. 35.6°C) but lower cardiac thermal tolerances (ABT: 30.5 vs. 35.1°C). Limpets from the cold coast site had higher acclimation responses in foot muscle CTmax (0.22°C per 1°C rise in acclimation) than those of the warm estuary site (0.07°C per 1°C rise in acclimation), but lower acclimation responses in cardiac thermal tolerance (ABT: -0.85°C per 1°C rise in acclimation) than those of the estuary site (ABT: 0.10°C per 1°C rise in acclimation). Since outer coast populations had lower cardiac plasticity and higher mortalities in the warm acclimation, we predict L. limatula from colder habitats will be more susceptible to rising temperatures. Our findings illustrate the importance of population-specific variation in short-term thermal plasticity when considering the effects of climate change on ectotherms.

Many of the morphological and physiological adaptations that marine mammals exhibit for an aquatic life enhance their ability to feed. Mysticeti use baleen to filter large numbers (e.g., swarms of krill or schools of fish) of smaller prey, while Odontoceti generally use raptorial biting and/or suction to capture larger, individual prey, often after pursuit. Some species of Phocidae and walruses rely primarily on suction feeding while most use raptorial biting. Sea otters use their fore paws to capture sessile invertebrates. Dugongs feed by scouring the seafloor, cropping leaves of seagrasses or uprooting the rhizomess. Manatees also have large facial muscles used for grazing and browsing. The mammary glands of marine mammals are relatively flat and lie beneath the blubber or skin. The availability of food is often unpredictable and episodic, so animals will often eat as much as possible and build body fat reserves when food is available. This behavior insures that they have sufficient energy for periods of anticipated or unanticipated fasting.

The relationships among the living classes of molluscs have remained contentious, in part because of a lack of consistent morphological characters that unequivocally unite clusters of taxa within this extremely disparate phylum. The osphradium, a chemosensory organ on or near the gills, is a putative potential synapomorphy of Mollusca. Although the osphradium regularly appears on illustrations of hypothetical unifying molluscan bauplans, the homology of these putative sensory structures has been debated in most classes. Considered examination of the evidence for homology based on development, ultrastructure, neural architecture, and function, demonstrates a lack of support for inferred homology among the varied structures described as ‘osphradia’. Neuroanatomical features are increasingly recognized as important for resolving deep phylogenetic divergences. The construction of morphological character sets for phylogenetic inference is dependent on robust determination of homology. Naming a structure does not underwrite its relationship to any other sensory organ. A fundamental assumption that one clade is ‘primitive’ may have biased the interpretation of anatomical results by early, and even some contemporary researchers, leaving the equality among important characters in doubt. Although these various sensory structures are no doubt real anatomical features, we question the assumption that there is a single molluscan osphradium and propose that at least two distinct classes of epithelial sensory structures have been identified as the molluscan osphradium. The complex suite of characters that describe the many varied sense organs in the mantle cavities of molluscs, may yet provide a foundation for neurophylogenetic insights to molluscan evolution.

We provide a size-based ontogenetic sequence of the development and differentiation of the lower reproductive tract of the heterobranch gastropod Helix aspersa (Muller 1774). Twelve development stages distributed among nine size classes were recognized based on readily visible changes in morphology and changes in tissue density. Geometric morphometrics was used to calculate the deformation between stages as represented by thin-plate spline bending energies. The developmental stages and sequence of developmental events are also compared to previously published scenarios for the evolution of stylommatophoran and other pulmonate reproductive tracts. These comparisons suggest that heterochronies, which include both acceleration and retardation, are operating in the morphological evolution of the pulmonate lower reproductive tract. This supports previous observations that largest number of developmental changes coincides with the transition to sexual maturity, which is also seen in the exponential curve of bending energies we observed in Helix aspersa. The belated organogenesis makes the ontogeny of the complex hermaphroditic reproductive system of pulmonates readily observable in size-friendly juveniles. This observation, coupled with the ease of raising individuals in the laboratory, recommends Helix aspersa as a potential model laboratory system for investigating molluscan evolutionary development.

Convergent evolution tends to lead to similar phenotypic responses to the same selective pressures. However, when the phenotypic response is polymorphic, it is less clear how evolutionary convergence can lead to parallel diversity across species and populations. The present study focuses on South American spiders in the genus Selkirkiella (Theridiidae), which are shown to be polymorphic for colour. We (1) examine the number of morphs and their correspondence across taxa and (2) place the phenomenon in a phylogenetic context to determine whether the colour polymorphism in Selkirkiella albogutatta from the Juan Fernandez archipelago represents a case of independent evolution and convergence, or whether there is common ancestry with other colour-polymorphic theridiids. Regarding the latter question, we also examine colour morphs in a related species (Selkirkiella luisi) from continental areas. We show that S. alboguttata and S. luisi have six and two morphs, respectively. The rank-order of morph frequencies in both species is approximately similar to that reported in other polymorphic theridiids. A molecular phylogeny supports previous work and shows that the colour polymorphism in Selkirkiella species appears to be a case of convergent evolution of a diverse colour polymorphism at the family level.

Nielsen and Meier (2002) are skeptical of our claim of phyletic information being present in the cell division patterns of spiralian taxa. They conclude that cell division patterns must be known in greater detail, and that coding methods for cell lineage data should be better refined before phyletic information can be identified. As noted by Nielsen and Meier (2002), earlier studies had focused almost exclusively on molluscan taxa. In addition, only one or two cell lineages had been typically considered, and none of these previous studies had used an explicit cladistic methodology to investigate potential phyletic information. Our analyses (as well as Nielsen and Meier's reanalysis of our data [2002, Fig. 1]) produce several groupings that were congruent with both molecular and morphological phylogenies. For example, we recovered an Oligochaete-leech clade, the sister relationship of the two Echiura species, and the overall structure of the gastropod mollusc clade. We also noted that the bivalve mollusc and annelid groupings in our tree were not monophyletic. However, the vast majority of the annelid taxa (Echiura + Polycheata + Pogonophora + Oligochaete + Leech) formed a grade outside the Polyplacophora + Gastropoda. Members of these groups were not randomly interdigitated within other taxa across the tree as would be expected if no phylogenetic information were present (as in the case of some polychaete worms and bivalve molluscs). Polyphyletic polychaetes, bivalves, and other worm groups have also been included in analyses of some molecular datasets so we were not that surprised by this result (e.g., Winnepenninckx et al. 1995). We reported the polyphyly in these and other groups (relative to traditional spiralian classifications) as part of our assessment of the degree of phylogenetic information remaining in cell lineage data. Like all characters, the cell lineage characters provided better resolution and more congruent information in some clades than they did in others. Nielsen and Meier (2002) suggest that our "puzzling phylogenetic results" might be partially explained by the coding of the cell division data into character states for cladistic analysis. Determining a metric by which to score cell lineage data is problematic. Absolute time from fertilization can vary greatly depending on temperature, and cleavage cycle is invariant with cell lineage and therefore noninformative. For our analysis we chose embryonic cell number, a standard comparative metric for spiralian embryos that dates from the late 1890s. More recently, cell number has been used for almost 20 years to argue acceleration and retardation of molluscan cell lineages during early development (e.g., Verdonk and Van den Biggelaar 1983; Freeman and Lundelius 1992; Haszprunar 1993; Van den Biggelaar 1993, 1996; Van den Biggelaar and Haszprunar 1996). For our cladistic analysis these same data were transformed into discrete character states by dividing the cell number by three. This was done to transform the cell number into a character state within PAUP's allowable range for ordered characters (31 steps; Swofford 1998). At that time we considered this to be a relatively assumption-free transformation as well as conservative because small variation in cell numbers would be grouped into a single state by rounding error (e.g., 23, 24, 25 cells would all be scored as state 8) rather than each given a unique state (e.g., Nielsen and Meier 2002, Fig. 2b). We do not doubt that homoplasy was present in the data, but this can be discovered only after the analysis, not a priori. The scenario constructed by Nielsen and Meier (2002) in their Figure 2 presents a similar problem for all studies using embryonic cell number as a metric, not just those that use a cladistic methodology. For example, contrary to Nielsen and Meier's (2002) interpretation, Van den Biggelaar and Haszprunar (1996) did not map developmental characters onto existing phylogenies. Instead, these latter two authors actually constructed alternative trees based on two characters presence or absence of the polar lobe and cell number at time of 4d formation, and we would suggest that Nielsen and Meier's (2002) scenario is much more problematic for these limited datasets than it is for our larger dataset in which all available data were included in the analysis. And, as with molecular data, it was anticipated that any robust phylogenetic signal would have to emerge from the background noise of homoplasy. Although we appreciate Nielsen and Meier's (2002) suggestion to instead map this data onto an existing tree, we wonder why they would accept our coding for mapping the characters but not for using them in the analysis itself. We consider Nielsen and Meier's suggested coding prohibitively restrictive in that differences early in cell lineages are propagated to later lineages. Their argument is that any upstream change in other connected lineages prohibits the downstream coding of similarity. For Nielsen and Meier (2002), although two cells may form at 32 cells, they should only be coded as similar (e.g., putatively homologous) if the

The seagrass limpet Tectura paleacea (Gastropoda; Patellogastropoda) belongs to a seagrass obligate lineage that has shifted from the Caribbean in the late Miocene, across the Isthmus of Panama prior to the closing of the Panamanian seaway, and then northward to its modern Baja California – Oregon distribution. To address whether larval entrainment by seagrass beds contributes to population structuring, populations were sampled at six California/Oregon localities approximately 2 degrees latitude apart during two post-settlement periods in July 2002 and June 2003. Partial cytochrome oxidase b (Cytb) sequences were obtained from 20 individuals (10 per year) from each population in order to determine the levels of population subdivision/connectivity. From the 120 individuals sequenced, there were eighty-one unique haplotypes, with the greatest haplotype diversity occurring in southern populations. The only significant genetic break detected was consistent with a peri-Point Conception (PPC) biogeographic boundary while populations north and south of Point Conception were each panmictic. The data further indicate that populations found south of the PPC biogeographic boundary originated from northern populations. This pattern of population structure suggests that seagrass patches are not entraining the larvae of T. paleacea by altering flow regimes within their environment; a process hypothesized to produce extensive genetic subdivision on fine geographic scales. In contrast to the haplotype data, morphological patterns vary significantly over very fine geographic scales that are inconsistent with the observed patterns of genetic population structure, indicating that morphological variation in T. paleacea might be attributed to differential ecophenotypic expression in response to local habitat variability throughout its distribution. These results suggest that highly localized conservation efforts may not be as effective as large-scale conservation efforts in near shore marine environments.

To distinguish between alternative explanations for the presence of synchronous broods in the Miocene-Pliocene bivalve, Transenriella species. we performed in situ burial experiments of the Recent species T. corfusa. All Recent Transennella species are asynchronous brooders; a single brood contains all or most developmental stages. Specimens from Miocene—Pliocene deposits of California suggest that some members of this taxon were synchronous brooders, i.e., all the embryos of a brood develop simultaneously with only one developmental stage represented at any time. The presence of synchronous Transennella broods in the Miocene—Pliocene could indicate that an evolutionary change in mode of reproduction has occurred in this genus. Alternatively, asynchronous brooding in this taxon may he conservative and preferential preservation of later stages of development, or seasonal variation in reproduction, could result in a taphonomic overprint. Our burial experiments indicate that the earliest stages of development are almost entirely lost; however. there is enough preservation of the later stages of development to distinguish the two modes of reproduction. Additionally. we discovered a single fossil specimen with an asynchronous brood. Based primarily on this specimen, and observations from the burial experiments, we conclude that the fossil synchronous broods are an artifact of preservation and asynchronous brooding in Transenella is conservative.

The story of the discovery and study of the Monoplacophora (or Tryblidia) and how they have contributed to our understanding of the evolution of the Mollusca highlights the importance of integrating data from the fossil record with the study of living forms. Monoplacophora were common in the early Paleozoic and were thought to have become extinct during the Devonian Period, approximately 375 Mya. In the mid 1950s, they were recovered from abyssal depths off of Costa Rica and were immediately heralded as a “living fossil.” The living specimens confirmed that some of the organs (kidneys, heart, and gills) were repeated serially, just like the shell muscles that had been observed in fossil specimens. This supported the hypothesis that they were closely related to other segmented organisms such as annelids and arthropods. Today, there are 29 described living species and a growing body of work examining their anatomy, phylogeny, and ecology. Additional fossil specimens have also been discovered, and what was once thought to be a possible missing link between annelid worms and mollusks now appears to be a highly specialized branch of the molluscan tree that tells us little about the ancestral mollusk condition. However, some assumptions and generalizations from those early days still remain—such as the abyssal nature of the living species. A large part of the evolutionary history of the lineage remains to be discovered and will likely prove more complicated and interesting than afforded by the living fossil designation.

L'examen de ce genre et des caracteres utilises par Bernard relevent des doutes sur l'ancetre commun de ces bivalves et l'utilite de regrouper ces taxons au niveau de la sous-famille. Les ressemblances utilisees par Bernard pour regrouper ces genres peuvent resulter de la convergence associee a la petite taille des individus

Protandric hermaphroditism, the sequential change from male to female, has been reported in several superfamilies of prosobranch gastropods including the Fissurellacea, Patellacea, Calyptraeacea, and Eulimacea (Webber, 1977). It is most common in members of the Calyptraeacea and the Patellacea. In the Calyptraeacea changes in sex are readily followed by observing copulative structures (Coe, 1944). Because patellacean limpets are predominantly broadcast spawners with external fertilization, external characters that can be used to determine the sex of individuals are rare. Hence, previous to this report the occurrence of protandry in most patellacean limpets has been based primarily on sexual dimorphism in size; the smaller size classes being made up of male individuals and the larger size classes of female individuals (Willcox, 1898; Orton, 1920, 1928; Orton, Southward & Dodd, 1956; Dodd, 1956; Branch, 1974). However, given this type of data it is often difficult to assess whether the observed sexual dimorphism is indicative of protandry or merely a result of differential growth and/or survival. The presence of simultaneous hermaphrodites in the intermediate size classes, as evidence of protandry is of limited value because simultaneous hermaphrodites occur sporadically in patellaceans that do not show a sexual dimorphism in size (Dodd, 1956; Branch, 1974). The only unambiguous way of proving the existance of protandry in patellacean limpets is the direct monitoring of gonadal changes in individuals through time. We report here the first direct observations of protandric hermaphroditism in a patellacean limpet.Lottia gigantea Sowerby, 1834 is a large (100 + mm), territorial, intertidal limpet that ranges from northern California to central Baja California, Mexico (Stimson, 1970).