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Oceans are home to much of the world's biodiversity, but we know little about the processes driving speciation in marine ecosystems with few geographical barriers to gene flow. Ecological speciation resulting from divergent natural selection between ecological niches can occur in the face of gene flow. Sister species in the young and ecologically diverse rockfish genus Sebastes coexist in the northeast Pacific, implying that speciation may not require geographical isolation. Here, I use a novel phylogenetic comparative analysis to show that rockfish speciation is instead associated with divergence in habitat depth and depth-associated morphology, consistent with models of parapatric speciation. Using the same analysis, I find no support for alternative hypotheses that speciation involves divergence in diet or life history, or that speciation involves geographic isolation by latitude. These findings support the hypothesis that rockfishes undergo ecological speciation on an environmental gradient.

G. G. Simpson, one of the chief architects of evolutionary biology's modern synthesis, proposed that diversification occurs on a macroevolutionary adaptive landscape, but landscape models are seldom used to study adaptive divergence in large radiations. We show that for Caribbean Anolis lizards, diversification on similar Simpsonian landscapes leads to striking convergence of entire faunas on four islands. Parallel radiations unfolding at large temporal scales shed light on the process of adaptive diversification, indicating that the adaptive landscape may give rise to predictable evolutionary patterns in nature, that adaptive peaks may be stable over macroevolutionary time, and that available geographic area influences the ability of lineages to discover new adaptive peaks.

Understanding how marine food webs are affected by anthropogenic stressors is an important steppingstone toward the improved management of natural resources. Stable isotope analysis of historical and modern samples spanning a century indicated that the niche width of an exploited fish community increased after the expansion of New Zealand fisheries. Since the 2000s most species increased their reliance on food webs supported by pelagic production, compared to coastal production supported by macroalgae, and shifted to a higher trophic level. Overall changes were coincident with ocean warming, climate oscillations, prey abundance and fishing intensity, but their effects were specific to each fish assemblage analyzed. Data derived from historical samples revealed how anthropogenic stressors can drive long-term shifts in the trophic structure of an exploited fish community.

If natural communities are assembled according to deterministic rules, coexisting species will represent a nonrandom subset of the potential species pool. We tested for signatures of assembly rules in the distribution of species' traits in Pacific rockfish (Sebastes spp.) assemblages. We used morphology, dietary niche (estimated with stable nitrogen isotopes), and distribution data to identify traits that relate to local-scale resource use (the α-niche) and to environmental gradients (the β-niche). We showed that gill raker morphology was related to trophic position (an α-niche axis), while relative eye size was associated with depth habitat (a β-niche axis). We therefore hypothesized that, within assemblages of coexisting rockfish species, the gill raker trait would be overdispersed (evenly spaced) due to limiting similarity, while relative eye size would be clustered due to environmental filtering. We examined the evolutionary relatedness of coexisting species to ask whether phylogenetic community structure and trait distributions gave similar indications about the roles of assembly processes. We tested the trait distributions and phylogenetic structure of 30 published rockfish assemblages against a null model of random community assembly. As predicted, the gill raker trait tended to be more evenly spaced than expected by chance, as did overall body size, while relative eye size was more clustered than expected. Phylogenetic community structure appeared to reflect historical dispersal and speciation and did not provide consistent support for assembly rules. Our results indicate that rockfish community assembly is nonrandom with regard to species' traits and show how distinguishing traits related to the α- and β-niches and incorporating functional morphology can provide for powerful tests of assembly rules.

Intraspecific trait variation may result from “carryover effects” of variability of environments experienced at an earlier life stage. This phenomenon is particularly relevant in partially migrating populations composed of individuals with divergent early life histories. While many studies have addressed the causes of partial migration, few have investigated the consequences for between‐individual variability later in life. We studied carryover effects of larval environment in a facultatively diadromous New Zealand fish, Gobiomorphus cotidianus, along an estuarine salinity gradient. We investigated the implications of varying environmental conditions during this critical stage of ontogeny for adult phenotype. We inferred past environmental history of wild‐caught adult fish using otolith microchemistry (Sr/Ca) as a proxy for salinity. We tested for main and interactive effects of larval and adult environment on a suite of traits, including growth rates, behavior (exploration and activity), parasite load, and diet (stable isotopes and gut contents). We found a Sr/Ca consistent with a continuum from freshwater to brackish environments, and with different trajectories from juvenile to adult habitat. Fish with Sr/Ca indicating upstream migration were more vulnerable to trematode infection, suggesting a mismatch to freshwater habitat. Diet analysis suggested an interactive effect of larval and adult environments on trophic position and diet preference, while behavioral traits were unrelated to environment at any life stage. Growth rates did not seem to be affected by past environment. Overall, we show that early life environment can have multiple effects on adult performance and ecology, with the potential for lifetime fitness trade‐offs associated with life history. Our study highlights that even relatively minor variation in rearing conditions may be enough to generate individual variation in natural populations. We investigated carryover effects of larval environment in a facultatively diadromous New Zealand fish, Gobiomorphus cotidianus. Using otolith microchemistry (Sr/Ca) as a proxy for salinity, we found that larval environment influence adult diet (stable isotopes and gut content) and parasitism, with a near significant effect on juvenile growth and no effect on adult behavior (exploration and activity).

A species's niche width reflects a balance between the diversifying effects of intraspecific competition and the constraining effects of interspecific competition. This balance shifts when a species from a competitive environment invades a depauperate habitat where interspecific competition is reduced. The resulting ecological release permits population niche expansion, via increased individual niche widths and/or increased among-individual variation. We report an experimental test of the theory of ecological release in three-spine stickleback (Gasterosteus aculeatus). We factorially manipulated the presence or absence of two interspecific competitors: juvenile cut-throat trout (Oncorhynchus clarki) and prickly sculpin (Cottus asper). Consistent with the classic niche variation hypothesis, release from trout competition increased stickleback population niche width via increased among-individual variation, while individual niche widths remained unchanged. In contrast, release from sculpin competition had no effect on population niche width, because increased individual niche widths were offset by decreased between-individual variation. Our results confirm that ecological release from interspecific competition can lead to increases in niche width, and that these changes can occur on behavioural time scales. Importantly, we find that changes in population niche width are decoupled from changes in the niche widths of individuals within the population.

ABSTRACT Stream periphyton is an ideal study system for explaining how dispersal shapes community patterns. Few studies have tried to investigate periphyton metacommunities at the reach scale, and studies comparing local versus upstream periphyton propagule sources are lacking. We aimed to address these knowledge gaps by disentangling environmental constraints and dispersal sources, including dispersal hypotheses related to periphyton functional guilds. We covered 25‐m sections of streambed with plastic silage cover sheets in three streams in Southern New Zealand, allowing river water to flow over the sheets. Samples on top of these sheets allowed periphyton colonisation only by drifting upstream propagules, while ‘control’ samples placed directly upstream of the plastic sheets were colonised by local and upstream propagules. We collected samples after 7, 14, and 25 days of colonisation. Response variables included periphyton biomass, community structure, and relative abundances of functional guilds. Control samples showed 1.5–6 times higher cell densities than plastic‐cover samples, suggesting that local colonisation is very important for biomass accrual. Periphyton communities on both tile types became more similar to each other with time, indicating that environmental filters overcame effects of colonisation sources. While motile and flagellated taxa showed the ability to reach their preferred microhabitats in all streams, the responses of the remaining functional guilds did not follow the expected patterns. We conclude that periphyton community assembly strongly depends on reach‐scale connectivity, which results in higher biomass accrual and community structure. These findings suggest that the mass effect paradigm is likely to be the principal metacommunity process shaping stream periphyton communities at the reach scale. Field experiment conducted to determine the role of local and upstream propagules as drivers of stream periphyton communities. Community composition, structure, and functional guilds were assessed. Local colonisation was identified as the primary propagule source, leading to a mass effect.

Variation in fitness across individuals is central to population growth, species coexistence and evolution by natural selection. Fitness variation associated with resource use is hugely consequential, but how this variation is generated and maintained within natural populations remains unclear. In particular, individual fitness may depend on many cumulative foraging decisions over time, but this hypothesis remains untested. We used multi‐tissue stable isotope analysis to determine isotopic niche trajectories within species, populations and sexes of thin‐toed frogs and explored how this temporal dimension of diet affects individual reproductive investment, body condition and parasite load. We found that individual frogs shifted their diets less than expected under a null model, likely due to functional trade‐offs that limit the incorporation of new prey types over time. However, within the observed range of diet shifts, individuals that modified their diet to a greater degree exhibited higher fitness, although this effect was sex‐dependent. We suggest that these different relationships between isotopic niche trajectory length and fitness within thin‐toed frogs are driven by variability in the resource environment, negative density dependence and allometric constraints. These strong fitness effects suggest that the temporal dimension of diet change is a potential target of natural selection and, therefore, could drive correlated evolution in phenotypic traits underlying diet flexibility. Our findings add a new level of complexity to the understanding of ecological and evolutionary consequences of niche variation by demonstrating that temporal variation in foraging consistency within populations leads to different fitness pay‐offs. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

ABSTRACT Exposed and isolated alpine ecosystems present evolutionary challenges for flying species worldwide. Many insects have undergone dramatic wing reduction in response to these harsh conditions, losing the ability to fly. By contrast, some taxa have countered alpine conditions by evolving larger wings to improve flight ability. In this study, we investigated how two independent clades of Zelandoperla fenestrata stoneflies respond to upland environments. Our results revealed strikingly different adaptations to elevation across the two closely related clades. In Clade 1 (southern South Island), wing length decreases sharply with increasing elevation. In contrast, wing length in the geographically adjacent Clade 2 (northern South Island, and North Island) increases with elevation. These contrasting strategies highlight the diverse adaptive pathways that may exist even for closely related lineages encountering similar environmental challenges. Alpine ecosystems present many challenges for flighted insects. Some insects have adapted to these conditions by undergoing dramatic wing reduction while others have evolved larger wings. Here we document both these contrasting adaptations to alpine life within a single insect species, illustrating how evolutionary outcomes are not always predictable based on phylogeny alone.

Landlocking of diadromous fish in freshwater systems can have significant genomic consequences. For instance, the loss of the migratory life stage can dramatically reduce gene flow across populations, leading to increased genetic structuring and stronger effects of local adaptation. These genomic consequences have been well‐studied in some mainland systems, but the evolutionary impacts of landlocking in island ecosystems are largely unknown. In this study, we used a genotyping‐by‐sequencing (GBS) approach to examine the evolutionary history of landlocking in common smelt (Retropinna retropinna) on Chatham Island, a small isolated oceanic island 800 kilometres east of mainland New Zealand. We examined the relationship between Chatham Island and mainland smelt and used coalescent analyses to test the number and timing of landlocking events on Chatham Island. Our genomic analysis, based on 21,135 SNPs across 169 individuals, revealed that the Chatham Island smelt was genomically distinct from the mainland New Zealand fish, consistent with a single ancestral colonisation event of Chatham Island in the Pleistocene. Significant genetic structure was also evident within the Chatham Island smelt, with a diadromous Chatham Island smelt group, along with three geographically structured landlocked groups. Coalescent demographic analysis supported three independent landlocking events, with this loss of diadromy significantly pre‐dating human colonisation. Our results illustrate how landlocking of diadromous fish can occur repeatedly across a narrow spatial scale, and highlight a unique system to study the genomic basis of repeated adaptation. Our genomic analysis, based on 21,135 SNPs across 169 individuals, revealed that the Chatham Island smelt was genomically distinct from the mainland New Zealand fish, consistent with a single ancestral colonisation event of Chatham Island in the Pleistocene. Significant genetic structure was also evident within the Chatham Island smelt, with a diadromous Chatham Island smelt group, along with three geographically structured landlocked groups. Coalescent demographic analysis supported three independent landlocking events, with this loss of diadromy significantly pre‐dating human colonisation.