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Abstract Thermal performance curves (TPCs) are important tools for predicting the sensitivity of populations to climate change. However, the interactive ways that temperature affects multiple life‐history components lead to different fitness outcomes. These interactions are poorly understood for modular animals, especially over the lifespan of individual colonies, which limits our capacity to connect physiological and demographic responses.The goal of this study was to assess and compare the relationships between temperature and different life‐history components in a modular animal to reveal the mechanisms underlying TPCs for fitness.We reared replicated clones of the marine bryozoanBugula neritinaacross a thermal gradient (16 values) ranging from 23 to 32°C, which reflected the upper thermal range of seasonal variation in the field. TPCs were constructed for survival (measured as zooids states within a colony), growth rate, development to reproductive maturity and reproductive capacity, which were measured over much of the realized lifespan expected under field conditions (~30 days).The effect of temperature was more acute on zooid states rather than whole‐colony survival, and increased temperature increased the frequency of polypide regression. Most colonies reached reproductive maturity up to ~30°C, but growth rate and reproduction decreased at temperatures beyond ~25°C. The decline in reproductive capacity over temperatures above ~25°C was then due to the decline in the production of zooids capable of brooding embryos and zooids transitioning to regressed states up until about 30°C and transitioning to dead state beyond that.Higher temperatures are often considered to affect reproduction by interfering with gametogenesis and post‐zygotic pathways, but in modular animals, changes in growth rate and module states could indirectly cause temperature sensitivity of reproduction. Our study has implications for the role of temperature in driving the sampled population's dynamics by setting the number of generations that occur during the time window when temperatures are conducive to reproduction. Our results also have implications for the generality and predictability of temperature on population persistence across unitary and modular animals. Read the freePlain Language Summaryfor this article on the Journal blog. 

Abstract Dispersal can evolve as an adaptation to escape competition with conspecifics or kin. Locations with a low density of conspecifics, however, may also lead to reduced opportunities for mating, especially in sessile marine invertebrates with proximity-dependent mating success. Since there are few experimental investigations, we performed a series of field experiments using an experimentally tractable species (the bryozoan Bugula neritina) to test the hypothesis that the density, spatial arrangement, and genetic relatedness of neighbours differentially affect survival, growth, reproduction, paternity, and sperm dispersal. We manipulated the density and relatedness of neighbours and found that increased density reduced survival but not growth rate, and that there was no effect of relatedness on survival, growth, or fecundity, in contrast to previous studies. We also manipulated the distances to the nearest neighbour and used genetic markers to assign paternity within known mother–offspring groups to estimate how proximity affects mating success. Distance to the nearest neighbour did not affect the number of settlers produced, the paternity share, or the degree of multiple paternity. Overall, larger than expected sperm dispersal led to high multiple paternity, regardless of the distance to the nearest neighbour. Our results have important implications for understanding selection on dispersal distance: in this system, there are few disadvantages to the limited larval dispersal that does occur and limited advantages for larvae to disperse further than a few 10s of metres. 

ABSTRACT Warming global temperatures have consequences for biological rates. Feeding rates reflect the intake of energy that fuels survival, growth and reproduction. However, temperature can also affect food abundance and quality, as well as feeding behavior, which all affect feeding rate, making it challenging to understand the pathways by which temperature affects the intake of energy. Therefore, we experimentally assessed how clearance rate varied across a thermal gradient in a filter-feeding colonial marine invertebrate (the bryozoan Bugula neritina). We also assessed how temperature affects phytoplankton as a food source, and zooid states within a colony that affect energy budgets and feeding behavior. Clearance rate increased linearly from 18°C to 32°C, a temperature range that the population experiences most of the year. However, temperature increased algal cell size, and decreased the proportion of feeding zooids, suggesting indirect effects of temperature on clearance rates. Temperature increased polypide regression, possibly as a stress response because satiation occurred quicker, or because phytoplankton quality declined. Temperature had a greater effect on clearance rate per feeding zooid than it did per total zooids. Together, these results suggest that the effect of temperature on clearance rate at the colony level is not just the outcome of individual zooids feeding more in direct response to temperature but also emerges from temperature increasing polypide regression and the remaining zooids increasing their feeding rates in response. Our study highlights some of the challenges for understanding why temperature affects feeding rates, especially for understudied, yet ecologically important, marine colonial organisms. 

Abstract Dispersal has far‐reaching implications for individuals, populations, and communities, especially in sessile organisms. Escaping competition with conspecifics and with kin are theorized to be key factors leading to dispersal as an adaptation. However, manipulative approaches in systems in which adults are sessile but offspring have behaviors is required for a more complete understanding of how competition affects dispersal. Here, we integrate a series of experiments to study how dispersal affects the density and relatedness of neighbors, and how the density and relatedness of neighbors in turn affects fitness. In a marine bryozoan, we empirically estimated dispersal kernels and found that most larvae settled within ~1 m of the maternal colony, although some could potentially travel at least 10s of meters. Larvae neither actively preferred or avoided conspecifics or kin at settlement. We experimentally determined the effects of spreading sibling larvae by manipulating the density and relatedness of settlers and measuring components of fitness in the field. We found that settler density reduced maternal fitness when settler neighbors were siblings compared with when neighbors were unrelated or absent. Genetic markers also identified very few half sibs (and no full sibs) in adults from the natural population, and rarely close enough to directly interact. In this system, dispersal occurs over short distances (meters) yet, in contrast with expectations, there appears to be limited kinship between adult neighbors. Our results suggest that the limited dispersal increases early offspring mortality when siblings settle next to each other, rather than next to unrelated conspecifics, potentially reducing kinship in adult populations. High offspring production and multiple paternity could further dilute kinship at settlement and reduce selection for dispersal beyond the scale of 10s of meters. 

Dispersal emerges as an outcome of organismal traits and external forcings. However, it remains unclear how the emergent dispersal kernel evolves as a by-product of selection on the underlying traits. This question is particularly compelling in coastal marine systems, where dispersal is tied to development and reproduction and where directional currents bias larval dispersal downstream, causing selection for retention. We modeled the dynamics of a metapopulation along a finite coastline using an integral projection model and adaptive dynamics to understand how asymmetric coastal currents influence the evolution of larval (pelagic larval duration) and adult (spawning frequency) life history traits, which indirectly shape the evolution of marine dispersal kernels. Selection induced by alongshore currents favors the release of larvae over multiple time periods, allowing long pelagic larval durations and long-distance dispersal to be maintained in marine life cycles in situations where they were previously predicted to be selected against. Two evolutionarily stable strategies emerged: one with a long pelagic larval duration and many spawning events, resulting in a dispersal kernel with a larger mean and variance, and another with a short pelagic larval duration and few spawning events, resulting in a dispersal kernel with a smaller mean and variance. Our theory shows how coastal ocean flows are important agents of selection that can generate multiple, often co-occurring evolutionary outcomes for marine life history traits that affect dispersal.