Trophic Niche Dynamics and Diet Partitioning of King Crab Lithodes santolla in Chile’s Sub-Antarctic Water

The southern king crab Lithodes santolla is one of the most economically important fishery species in the southern waters of the Atlantic and Pacific Oceans. A combination of stomach content and stable isotope analyses was used to reveal the potential dietary characteristics, isotopic niche, overlap among maturity stages and sexes, and trophic relationships of an L. santolla population in the Nassau Bay, Cape Horn region. Stable isotope analyses indicated that L. santolla assimilated energy from a basal carbon source, the giant kelp Macrocystis pyrifera, forming the trophic baseline of the benthic food web. Moreover, the trophic position of L. santolla varied among late juveniles and adults, suggesting that the southern king crab does undergo an ontogenetic diet shift. L. santolla exhibited intraspecific isotopic niche variation, reflecting niche differentiation which allows the species to partition resources. The trophic relationships of L. santolla with the associated fauna suggested some potential interactions for food resources/habitat use when they are limited. This study is the first attempt to characterize the trophic dynamics of the southern king crab in the Cape Horn area and, by generating more data, contributes to the conservation of the king crab population and the long-term management of local fisheries that rely on this resource.

Climate warming may increase the frequency of cold-adapted haplotypes in alpine plants

Modelling of climate-driven range shifts commonly treats species as ecologically homogeneous units. However, many species show intraspecific variation of climatic niches and theory predicts that such variation may lead to counterintuitive eco-evolutionary dynamics. Here, we incorporate assumed intraspecific niche variation into a dynamic range model and explore possible consequences for six high-mountain plant species of the European Alps under scenarios of twenty-first century climate warming. At the species level, the results indicate massive range loss independent of intraspecific variation. At the intraspecific level, the model predicts a decrease in the frequency of warm-adapted haplotypes in five species. The latter effect is probably driven by a combination of leading-edge colonization and priority effects within the species’ elevational range and was weakest when leading-edge expansion was constrained by mountain topography The resulting maladaptation may additionally increase the risk that alpine plants face from shrinkage of their ranges in a warming climate.

Macroevolutionary Changes of Plants on Islands

<p>Insularity is known to produce predictable evolutionary changes in plants. For example, herbaceous plants often evolve woodiness and seeds tend to have reduced dispersal capabilities on islands. However, our understanding of how other plant traits may evolve on islands is lacking. Furthermore, plants are modular organisms and by investigating evolutionary changes in specific plant traits we may better understand macroevolutionary processes on islands. In this thesis, I investigate evolutionary changes in a range of plant traits on islands. First, I tested for evolutionary changes in seed size on islands (Chapter 2). Island plants consistently produced larger seeds than mainland relatives. Furthermore, this result was consistent regardless of differences in dispersal mode, growth form and evolutionary history. Selection may favour increased seed size to reduce dispersal distances. Additionally, selection may favour larger seeds due to the competitive advantage conferred to developing seedlings. Many animal taxa exhibit increased sexual size dimorphism (SSD) on islands, as predicted by the niche variation hypothesis. However, patterns of SSD among dioecious plants on islands are unknown. In Chapter 3 I tested for differences in SSD of dioecious plants that colonized four island groups from New Zealand (mainland). The degree of SSD did not vary predictable between island and mainland plants, contrary to predictions of the niche variation hypothesis. However, SSD was consistently female biased on the mainland and results suggest selection is acting to increase the size of both sexes on islands. Evolutionary changes in island plants may be a response to herbivory by unique large browsers. For example, the divaricate growth form is common in the New Zealand flora and may have deterred browsing moa. In Chapter 4 I tested for differences in traits associated with the divaricate growth form between plants from mainland New Zealand and Chatham Island. Results suggest that an absence of moa on Chatham Island has relaxed selection for traits associated with the divaricate growth form. An emerging body of research suggests aposematism (warning signals to herbivores) may be common in plants. However, previous investigations have not appreciated the fact that the perspective of terrestrial herbivores changes as plants grown vertically. Furthermore, ontogenetic changes in the capacity of plants to defend themselves may influence the reliability of warning signals. In Chapter 5 I tested for ontogenetic changes in two potentially aposematic signals produced by Pseudopanax crassifolius. Aposematism on upper leaf surfaces peaked early in ontogeny, providing a dishonest signal of defense. Conversely, signaling on the underside of leaves peaked later in ontogeny and scaled positively with structural defenses. The results of this thesis suggest selection is acting on specific plant traits on islands. Evolutionary pathways, such as the evolution of woodiness, may be better explained by considering selection acting on other plant traits. For example, selection acting on seed size may facilitate evolutionary size changes evident at later life-history stages. A lack of consensus exists regarding the role of insular herbivores in the evolution of island plants. The results of Chapters 4 and 5 suggest herbivory has played an important role in the evolution of novel morphology of island plants. Considering trait specific changes of plants on islands may further our understanding of prominent evolutionary pathways by pinpointing the action of selection.</p>

Relationships Among Trophic Niche Width, Morphological Variation, and Genetic Diversity of Hemiculter leucisculus in China

According to the niche variation hypothesis (NVH), the populations with wider niches are phenotypically more variable than those with narrow niches. Giller expanded the NVH, suggesting that the niche width, morphological variation, and genetic diversity are all positively correlated. However, the hypothesis has been a subject of debate and discussion. In the present study, the NVH was tested by analyzing the relationships among trophic niche width, morphological variation, and genetic diversity of Hemiculter leucisculus, a widespread cyprinid fish. The fish samples were collected from six sites across Haihe, the Yellow, and the Yangtze River basins in China. The relationships among trophic niche width, morphological variation, and genetic diversity were analyzed using Pearson correlation at the inter-population level. Our analysis indicated that trophic niche width is significantly positively correlated with morphological variation, which corroborates the NVH. Morphological variation was significantly correlated to genetic diversity. However, no relationship was observed between trophic niche width and genetic diversity. We inferred that the dietary niche of H. leucisculus might change due to the plastic response toward environmental changes rather than due to the genetic variation. We also suggest that the effects of environment and heredity on the niche of the freshwater fish should be quantified separately in further studies.

Evolution and functional dynamics of dehydrins in model Brachypodium grasses

Dehydration proteins (dehydrins, DHNs) confer tolerance to water-stress deficit to plants, thus playing a fundamental role in plant response and adaptation to water-deprivation stressful environments. We have performed a comparative genomics and evolutionary study of DHN genes in four model Brachypodium grass species, and a drought-induced functional analysis in 32 ecotypes of the flagship species B. distachyon, to gain insight into the origins and dynamics of these proteins and the correlated drought-mediated phenotypic responses in ecotypes showing different hydric requirements. Genomic sequence analysis detected 10 types of dehydrin genes (Bdhn) across the Brachypodium species, totalling 47 genes. Domain and conserved motif contents of peptides encoded by Bdhn genes revealed eight protein architectures, YSɸK2 being the most common architecture. Bdhn genes were spread across several chromosomes and more frequent in syntenic chromosomes 3 and 4 of B. distachyon, 4 and 5 of B. stacei and 4 of B. sylvaticum. Tandem and segmental duplication events were detected for four Bdhn genes. Selection analysis indicated that all the Bdhn genes were constrained by purifying selection. Three upstream cis-regulatory motifs (BES1, MYB124, ZAT) were consistently detected in several Bdhn genes. Functional analysis in 32 natural accessions of B. distachyon demonstrated that only four Bdhn genes (Bdhn1, Bdhn2, Bdhn3, Bdhn7) were expressed in mature leaves and that all of them were significantly more highly expressed in plants under drought conditions. These genes corresponded to wheat orthologs that were also significantly more expressed under drought stress. Brachypodium dehydrin expression was significantly correlated with drought-response phenotypic traits (plant biomass, leaf carbon and proline contents and WUE increases, leaf water and nitrogen content changes) being more pronounced in drought-tolerant ecotypes. Bdhn expression, associated phenotypic trait changes and climate niche variation did not show significant phylogenetic signal when tested in the B. distachyon genealogical-species tree. By contrast, some of them showed low or marginal significant phylogenetic signal when tested in the B. distachyon Bdhn tree, suggesting that Bdhn gene evolution is partially related to adaptation to drought in this species. Our results demonstrate that dehydrin composition and regulation is a key factor determining the acquisition of water-stress tolerance in grasses.

Comparative analysis of diversity and environmental niches of soil bacterial, archaeal, fungal and protist communities reveal niche divergences along environmental gradients in the Alps

Although widely used in ecology, comparative analyses of diversity and niche properties are still lacking for microorganisms, especially concerning niche variations. In this study, we identified important topoclimatic, edaphic, spatial and biotic drivers of the alpha and beta diversity of bacterial, archaeal, fungal and protist communities. Then, we calculated the niche breadth and position of each taxon along environmental gradients within all taxonomic groups, to determine how these vary within and between groups. Quantifying the niches of microbial taxa is necessary to then forecast how taxa and the communities they compose might respond to environmental changes. We found that edaphic properties were the most important drivers of both community diversity and composition for all microbial groups. Protists presented the largest niche breadths, followed by bacteria and archaea, with fungi displaying the smallest. Niche breadth generally decreased towards environmental extremes, especially along edaphic gradients, suggesting increased specialisation of microbial taxa in highly selective environments. Overall, we showed that microorganisms have well defined niches, as do macro-organisms, likely driving part of the observed spatial patterns of community variations. Assessing niche variation more widely in microbial ecology should open new perspectives, especially to tackle global change effects on microbes.

Individual environmental niches in mobile organisms

Individual variation is increasingly recognized as a central component of ecological processes, but its role in structuring environmental niche associations remains largely unknown. Species’ responses to environmental conditions are ultimately determined by the niches of single individuals, yet environmental associations are typically captured only at the level of species. Here, we develop scenarios for how individual variation may combine to define the compound environmental niche of populations, use extensive movement data to document individual environmental niche variation, test associated hypotheses of niche configuration, and examine the consistency of individual niches over time. For 45 individual white storks (Ciconia ciconia; 116 individual-year combinations), we uncover high variability in individual environmental associations, consistency of individual niches over time, and moderate to strong niche specialization. Within populations, environmental niches follow a nested pattern, with individuals arranged along a specialist-to-generalist gradient. These results reject common assumptions of individual niche equivalency among conspecifics, as well as the separation of individual niches into disparate parts of environmental space. These findings underscore the need for a more thorough consideration of individualistic environmental responses in global change research.

Individualised niches: an integrative conceptual framework across behaviour, ecology, and evolution

Individuals differ. This seemingly trivial statement has nevertheless led to paradigm shifts, as three different fields of organismal biology have seen a marked change in key concepts over the past few decades. In animal behaviour, it has increasingly been realised that behavioural differences among individuals can be stable over time and across contexts, giving rise to the concept of animal personalities. In ecology, an increasing focus is likewise on the considerable variation in the ecological niche realised by species, populations, and individuals, giving rise to the concept of niche specialisation or individual niche variation. In evolutionary biology, where individual variation has always been central, there is an increasing awareness of the complexity with which individuals interact with the environment in producing unique phenotypes. Recent theoretical and empirical work has highlighted that the fitness landscape is rather complex, with multiple fitness peaks. It depends on the individual with its genotype, in interaction with its specific environment, which local or global fitness peak is attainable. Over the past 15 years, the need for more integrated conceptual frameworks transcending disciplines has been voiced ever more strongly. Whereas initially the ecological time scale was deemed to be fundamentally different from the evolutionary one, this notion has recently been replaced by a more integrative one, where evolution can indeed happen over ecological time scales. While in each of the three fields behaviour, ecology, and evolution, the concept of individualisation has contributed to major scientific progress, sufficient cross-fertilisation is lacking. Here, we propose a new level of conceptual unification: the individualised niche. By merging the niche concept with the fitness and animal personality concepts, new explanatory power for both ecological and evolutionary processes emerges.