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Climate change is not only causing steady increases in average global temperatures but also increasing the frequency with which extreme heating events occur. These extreme events may be pivotal in determining the ability of organisms to persist in their current habitats. Thus, it is important to understand how quickly an organism's heat tolerance can be gained and lost relative to the frequency with which extreme heating events occur in the field. We show that the California mussel, Mytilus californianus -a sessile intertidal species that experiences extreme temperature fluctuations and cannot behaviourally thermoregulate-can quickly (in 24-48 h) acquire improved heat tolerance after exposure to a single sublethal heat-stress bout (2 h at 30 or 35°C) and then maintain this improved tolerance for up to three weeks without further exposure to elevated temperatures. This adaptive response improved survival rates by approximately 75% under extreme heat-stress bouts (2 h at 40°C). To interpret these laboratory findings in an ecological context, we evaluated 4 years of mussel body temperatures recorded in the field. The majority (approx. 64%) of consecutive heat-stress bouts were separated by 24-48 h, but several consecutive heat bouts were separated by as much as 22 days. Thus, the ability of M. californianus to maintain improved heat tolerance for up to three weeks after a single sublethal heat-stress bout significantly improves their probability of survival, as approximately 33% of consecutive heat events are separated by 3-22 days. As a sessile animal, mussels likely evolved the capability to rapidly gain and slowly lose heat tolerance to survive the intermittent, and often unpredictable, heat events in the intertidal zone. This adaptive strategy will likely prove beneficial under the extreme heat events predicted with climate change.

Complex life cycles characterized by uncertainty at transitions between larval/juvenile and adult environments could favour irreversible physiological plasticity at such transitions. To assess whether thermal tolerance of intertidal mussels ( Mytilus californianus ) adjusts to post-settlement environmental conditions, we collected juveniles from their thermally buffered microhabitat from high- and low-shore locations at cool (wave-exposed) and warm (wave-protected) sites. Juveniles were transplanted to unsheltered cages at the two low sites or placed in a common garden. Juveniles transplanted to the warm site for one month in summer had higher thermal tolerance, regardless of origin site. By contrast, common-garden juveniles from all sites had lower tolerance indistinguishable from exposed site transplants. After six months in the field plus a common garden period, there was a trend for higher thermal tolerance at the protected site, while reduced thermal tolerance at both sites indicated seasonal acclimatization. Thermal tolerance and growth rate were inversely related after one but not six months; protected-site transplants were more tolerant but grew more slowly. In contrast to juveniles, adults from low-shore exposed and protected sites retained differences in thermal tolerance after common garden treatment in summer. Both irreversible and reversible forms of plasticity must be considered in organismal responses to changing environments., (© 2018 The Author(s).)

The mussel Mytilus californianus is a dominant competitor for space on wave-swept rocky shores, where it forms dense beds. Byssal threads anchor each mussel both to the substratum and to neighbors, allowing mussels to resist the onslaught of waves. When incident hydrodynamic stress exceeds a mussel's tenacity, the threads are broken, the mussel is dislodged, and a gap is opened in the bed. Here, we show that when groups of contiguous bed mussels experience similar hydrodynamic forces, they collectively have a lower tenacity than when force is applied to a single individual. Lowered group tenacity leads to greater probabilities of dislodgment, with ramifications for community dynamics and species diversity., (© 2014 Marine Biological Laboratory.)

The invasive marine mussel Mytilus galloprovincialis has displaced the native congener Mytilus trossulus from central and southern California, but the native species remains dominant at more northerly sites that have high levels of freshwater input. To determine the extent to which interspecific differences in physiological tolerance to low salinity might explain limits to the invasive species' biogeography, we used an oligonucleotide microarray to compare the transcriptional responses of these two species to an acute decrease in salinity. Among 6777 genes on the microarray, 117 genes showed significant changes that were similar between species, and 12 genes showed significant species-specific responses to salinity stress. Osmoregulation and cell cycle control were important aspects of the shared transcriptomic response to salinity stress, whereas the genes with species-specific expression patterns were involved in mRNA splicing, polyamine synthesis, exocytosis, translation, cell adhesion, and cell signalling. Forty-five genes that changed expression significantly during salinity stress also changed expression during heat stress, but the direction of change in expression was typically opposite for the two forms of stress. These results (i) provide insights into the role of changes in gene expression in establishing physiological tolerance to acute decreases in salinity, and (ii) indicate that transcriptomic differences between M. galloprovincialis and M. trossulus in response to salinity stress are subtle and involve only a minor fraction of the overall suite of gene regulatory responses., (© 2010 Blackwell Publishing Ltd.)

Populations of most marine organisms are connected by the dispersal of larval stages, with profound implications for marine conservation. Because of the extreme effort needed to empirically measure larval exchange, multispecies conservation efforts must estimate connectivity by extrapolation using taxonomy, adult distribution, life history, behavior, or phenology. Using a 6-year record of connectivity realized through trace-elemental fingerprinting of larval shells, we document the seasonal and interannual variability of larval exchange for two congeneric mussel species with overlapping but distinct distribution, life history, and reproduction timing. We reveal consistent autumn poleward movement and spring equatorward movement for both species, coincident with near-shore surface currents. However, because the major reproductive seasons differ, the dominant source-sink dynamics of these two congeneric species are nearly opposite. Consideration of present and future reproductive timing as altered by climate change is crucial to marine connectivity and conservation, especially for the numerous coastal areas subject to seasonal current reversals., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Recent work demonstrates that nearshore oceanography can generate strong variation in the delivery of resources (nutrients and larvae) to benthic marine communities over spatial scales of tens to hundreds of kilometers. Moreover, variation in the strength of these bottom-up inputs is often spatially consistent, linked to regional centers of upwelling, coastal topography, and other stable features of the coastline. Whereas the ecological effects of these oceanographic links are increasingly clear, the possibility that these same bottom-up forces might impose spatially varying selection on consumers has not been addressed. Here, we test the hypothesis that a carnivorous snail (Nucella canaliculata) with direct development is locally adapted to persistent differences in prey recruitment within two adjacent oceanographic regions (northern California and Oregon, USA). Previous laboratory studies demonstrated that snails from Oregon rarely drilled the thick-shelled mussel Mytilus californianus, whereas snails from California readily drilled this prey. To test whether these differences reflect local adaptation, snails from two populations in each region were raised through two laboratory generations to minimize the potential influence of nongenetic effects. We then reciprocally outplanted these F2 generation snails to field enclosures at each of the four sites and monitored their growth for 11 months. Recruitment and availability of preferred prey (the acorn barnacle Balanus glandula and blue mussel Mytilus trossulus) at the experimental sites were 1-3 orders of magnitude lower in California than in Oregon. At the California sites, snails that originated from Oregon sources failed to drill larger M. californianus, encountered few alternative prey, and showed almost no growth. In contrast, snails from California drilled M. californianus and showed substantial growth. These results strongly suggest that the capacity of California snails to drill M. californianus allows these snails to succeed in an oceanographic region where the recruitment of alternative, preferred prey is low. More broadly, our results suggest that persistent spatial variation in recruitment and other oceanographically mediated processes may lead to adaptive differentiation among populations of consumers in adjacent coastal regions.

The extent to which community processes can be generalized from local field studies to larger spatial scales remains a contentious issue. The search for broad generality can be hampered when species interactions vary geographically, a common phenomenon attributed to a wide range of underlying ecological factors. Less attention has been directed toward understanding the additional role that evolutionary processes may play in modifying the way that pairs of species interact over large spatial scales. Here we examine whether marked geographic variation in the interaction between a predatory snail (Nucella canaliculata) and an intertidal mussel (Mytilus californianus) arises from phenotypic plasticity or fixed genetic differences among snail populations. Over a three-year period, we reared snails from eight populations in California and Oregon, USA, through two laboratory generations and tested whether family lines differed in their ability to drill M. californianus. Remarkably, F2 generation snails from Oregon sources were generally unable to drill mid-sized Mytilus californianus (5-7 cm long), whereas snails from California readily drilled this prey. Because snails were raised through two generations on a common diet (Mytilus trossulus), these differences among populations likely have a genetic basis. Snails from California and Oregon readily interbred and produced viable offspring in the laboratory, suggesting that populations belong to a single biological species. Field surveys of mussel beds revealed striking geographic variation in predation that closely matched the observed differences in the drilling capacity of N. canaliculata. Drilled M. californianus were common at all sites in California and included many large mussels (> 10 cm long). In contrast, drilled M. californianus were rare on the central Oregon coast and consisted mostly of small mussels (< 3 cm). We hypothesize that persistent variation in prey recruitment along the coast has selected for interpopulation differences in the drilling capacity of this direct-developing snail, with potential consequences for the size structure of mussel beds. Combined with growing evidence of restricted gene flow and low connectivity among many marine populations, this study highlights the importance of considering the contribution of evolutionary processes to geographic variation in species interactions.

Based on the belief that marine larvae, which can spend days to months in the planktonic stage, could be transported considerable distances by ocean currents, it has long been assumed that populations of coastal species with a planktonic larval stage are demographically open and highly "connected." Such assumptions about the connectivity of coastal populations govern approaches to managing marine resources and shape our fundamental understanding of population dynamics and evolution, yet are rarely tested directly due to the small size and high mortality of marine larvae in a physically complex environment. Here, we document a successful application of elemental fingerprinting as a tracking tool to determine sources of settled invertebrates and show that coastal mussel larvae, previously thought to be highly dispersed, can be retained within 20-30 km of their natal origin. We compare two closely related and co-occurring species, Mytilus californianus and Mytilus galloprovincialis, and determine that, despite expected similarities, they exhibit substantially different connectivity patterns. Our use of an in situ larval culturing technique overcomes the previous challenge of applying microchemical tracking methods to species with completely planktonic development. The exchange of larvae and resulting connectivities among marine populations have fundamental consequences for the evolution and ecology of species and for the management of coastal resources.