The Biological Bulletin

Physiological processes influence how individuals perform in various environmental contexts. The basis of such processes, metabolism, scales allometrically with body mass and nonlinearly with temperature, as described by a thermal performance curve. Past studies of thermal performance curves tend to focus on effects of temperature on a single body size or population, rather than variation in the thermal performance curve across sizes and populations. Here, we estimate intraspecific variation in parameters of the thermal performance curve in the salt marsh gastropod Littoraria irrorata. First, we quantify the thermal performance curve for respiration rate as a function of both temperature and body size in Littoraria and evaluate whether the thermal parameters and body size scaling are interdependent. Next, we quantify how parameters in the thermal performance curve for feeding rate vary between three Littoraria populations that occur along a latitudinal gradient. Our work suggests that the thermal traits describing Littoraria respiration are dependent on body mass and that both the thermal traits and the mass scaling of feeding vary across sites. We found limited evidence to suggest that mass scaling of Littoraria feeding or respiration rates depends on temperature. Variation in the thermal performance curves interacts with the size structure of the Littoraria population to generate divergent population-level responses to temperature. These results highlight the importance of considering variation in population size structure and physiological allometry when attempting to predict how temperature change will affect physiological responses and consumer-resource interactions.

Most organisms are faced with daily cyclic changes in a suite of environmental conditions, including temperature. In shallow marine waters, populations of the same species may experience either intertidal or subtidal conditions, such that some individuals experience extreme daily fluctuations as the tide ebbs and flows, while others only a few meters away experience less pronounced or less frequent fluctuations or almost constant thermal conditions. This study used a fully factorial combination of three thermal treatments and two diet treatments to test the hypotheses that (1) individuals experiencing fluctuating temperatures perform more poorly than those experiencing the same mean temperature under constant conditions and that (2) the negative impact of fluctuating temperatures is greater under food-limiting conditions. Five life-history components of the slipper snail Crepidula cf. marginalis were used as response variables. We found that temperature fluctuations impacted size at hatching and time to hatching, as well as growth rate, to some extent. Diet treatments impacted growth rates, clutch sizes, time to first brood, and time to hatching. There were no statistically significant interactions between the two factors. These results show that fluctuations between two temperatures that are typically experienced by these animals in the field can significantly affect fitness-related characters and, therefore, suggest the tidal height at which larvae settle can significantly impact individual fitness. This is one of the first studies to demonstrate that differences in the frequency of fluctuations, in the absence of differences in the magnitude or the mean, can have significant impacts on invertebrate life histories.

Zebra mussels (Dreissena polymorpha), first reported in Texas during 2009, have infested 28 Texas reservoirs over 11 years. This species has not previously invaded water bodies as warm as those in Texas, where temperatures approach or exceed its previously accepted incipient upper thermal limit of 30 °C, raising the question of how such temperatures impact its population dynamics. Over 3–5 years, monthly collections of mussels, sampling for planktonic mussel veligers, juvenile settlement data, and water quality parameters, were undertaken at Texas lakes Texoma, Ray Roberts, and Belton to estimate mussel shell length growth rates, life spans, reproductive periods, and settlement patterns. Biannual spawning periods occurred at water temperatures of 18 to 28 °C, resulting in distinct spring and fall juvenile settlement cohorts. Growth rates were rapid, with both cohorts attaining mean maximum shell lengths of 20–25 mm within 8–15 months of settlement, compared to European and northeastern US populations that attained similar sizes after 2–4 years. Shortened life spans were demarcated by adult mussel die-offs during summer months of elevated water temperature the year after initial settlement, leading to short-term cyclical fluctuations in population densities. Large-scale mussel die-offs were caused by flooding and hypoxia events. Elevated temperatures appeared to facilitate mussel invasiveness by increasing spawning frequency and elevating growth rates, thus reducing time to maturity and allowing population recovery within 1–2 years after environmentally induced severe population declines.

The calyptraeids Crepidula adunca and Crepidula norrisiarum, both direct developers, are abundant in the shallow waters of the northeastern Pacific. They have long been considered as two allopatric species that live on different hosts and differ in body size. In this study, we rigorously test this historical hypothesis by assessing molecular taxonomy, museum records, new morphological and host observations, and population genetic structure along the northeast Pacific coast. Results show that, contrary to previous understanding, the distributions of the two species largely overlap and that size does not effectively distinguish them, especially in the northern part of the range where the nominal “C. adunca” has been studied. Newly recognized northern occurrences of C. norrisiarum demonstrate that both species have similar, disrupted distributions that range from British Colombia through southern California. Neither species is reported to occur on the outer shores of southern Washington or Oregon, the exception being records of C. adunca at Cape Arago, Oregon. Despite this apparent geographic gap, neither species shows appreciable genetic differentiation between the northern and southern parts of its ranges. Despite body size having been used to distinguish these species, our observations do not support body size as a species-specific trait; rather, they support a new hypothesis that body size variation reflects regional differences in host use and host availability.

The Atlantic slipper limpet, Crepidula fornicata, is a sequential hermaphrodite whose size at sex change is plastic with respect to social and population cues. As an organism allocates energy between growth, reproduction, and maintenance, the increased cost of one process may affect another. Thus, C. fornicata affected by a stressor might have to alter the balance of energy allocation, potentially leading to changes in the timing of sex change. One such biotic stressor, the boring sponge Cliona celata, has been demonstrated to affect growth and condition of numerous molluscs. In this study, we explored whether the presence of the boring sponge affected the rate of sex change for C. fornicata, using both field surveys and an in situ manipulation. Population surveys suggested that while boring sponges may reduce tissue condition of slipper limpets, this relationship is highly variable and likely confounded by site variables. Using population metrics (size at sex, L₅₀), the presence of a boring sponge did not appear to affect sex change. Likewise, during the in situ experiment where we manipulated stack sex ratios, we did not find any differences in the timing of sex change between male-male and male-female stacks, even though C. fornicata without sponges grew significantly faster. Thus, results from field surveys and our in situ experiment suggest that sex change in this species appears robust to biotic stressors. This study suggests that C. fornicata will undergo sex change when conditions dictate, even if it is experiencing some level of biotic stress, a strategy that likely allows it to maximize lifetime reproductive output.

Cephalopods use dynamic camouflage to blend in with their environment, communicate with conspecifics, and mimic other animals by changing their skin’s color, texture, pattern, and shape. Past studies have cataloged common body patterns presented by various cephalopod species to gain insight into the evolution and function of these patterns in the natural environment. The common (Sepia officinalis), pharaoh (Sepia pharaonis), and flamboyant (Metasepia pfefferi) cuttlefish are three of the previously studied species and demonstrate that differences in habitat, physical size, and evolutionary history may influence the capacity and usage of body patterning. We studied the body patterns of an additional cuttlefish species, the dwarf cuttlefish (Sepia bandensis), to investigate further what aspects of ecology or behavior may influence body patterning in cuttlefish. We captured still images and video recordings of individually housed dwarf cuttlefish and analyzed them to catalog the body pattern components displayed. We utilized a quantitative approach to determine body patterns through a maximum likelihood analysis program (AutoClass C). We identified 79 distinct body pattern components, including 8 newly described components, and 7 overall body patterns. Our findings on the body patterning behavior of the dwarf cuttlefish add to a growing database of cephalopod display patterns for future studies and provide insight into the ecological and evolutionary drivers of dynamic camouflage in cephalopods.