Unlabelled: Discerning ecosystem change and food web dynamics underlying anthropogenic eutrophication and the introduction of non-native species is necessary for ensuring the long-term sustainability of fisheries and lake biodiversity. Previous studies of eutrophication in Lake Victoria, eastern Africa, have focused on the loss of endemic fish biodiversity over the past several decades, but changes in the plankton communities over this same time remain unclear. To fill this gap, we examined sediment cores from a eutrophic embayment, Mwanza Gulf, to determine the timing and magnitude of changes in the phytoplankton and zooplankton assemblages over the past century.
View Article and Find Full Text PDFLake Victoria is well known for its high diversity of endemic fish species and provides livelihoods for millions of people. The lake garnered widespread attention during the twentieth century as major environmental and ecological changes modified the fish community with the extinction of approximately 40% of endemic cichlid species by the 1980s. Suggested causal factors include anthropogenic eutrophication, fishing, and introduced non-native species but their relative importance remains unresolved, partly because monitoring data started in the 1970s when changes were already underway.
View Article and Find Full Text PDFTropical freshwater lakes are well known for their high biodiversity, and particularly the East African Great Lakes are renowned for their adaptive radiation of cichlid fishes. While comparative phylogenetic analyses of extant species flocks have revealed patterns and processes of their diversification, little is known about evolutionary trajectories within lineages, the impacts of environmental drivers, or the scope and nature of now-extinct diversity. Time-structured palaeodata from geologically young fossil records, such as fossil counts and particularly ancient DNA (aDNA) data, would help fill this large knowledge gap.
View Article and Find Full Text PDFAdaptive radiations have been instrumental in generating a considerable amount of life's diversity. Ecological opportunity is thought to be a prerequisite for adaptive radiation, but little is known about the relative importance of species' ecological versatility versus effects of arrival order in determining which lineage radiates. Palaeontological records that could help answer this are scarce.
View Article and Find Full Text PDFAntarctic notothenioid fishes are recognised as one of the rare examples of adaptive radiation in the marine system. Withstanding the freezing temperatures of Antarctic waters, these fishes have diversified into over 100 species within no more than 10-20 million years. However, the exact species richness of the radiation remains contested.
View Article and Find Full Text PDFEvolution can repeat itself, resulting in parallel adaptations in independent lineages occupying similar environments. Moreover, parallel evolution sometimes, but not always, uses the same genes. Two main hypotheses have been put forth to explain the probability and extent of parallel evolution.
View Article and Find Full Text PDFThe field of paleolimnology has made tremendous progress in reconstructing past biotic and abiotic environmental conditions of aquatic ecosystems based on sediment records. This, together with the rapid development of molecular technologies, provides new opportunities for studying evolutionary processes affecting lacustrine communities over multicentennial to millennial timescales. From an evolutionary perspective, such analyses provide important insights into the chronology of past environmental conditions, the dynamics of phenotypic evolution, and species diversification.
View Article and Find Full Text PDFThe types of mutations affecting adaptation in the wild are only beginning to be understood. In particular, whether structural changes shape adaptation by suppressing recombination or by creating new mutations is unresolved. Here, we show that multiple linked but recombining loci underlie cryptic color morphs of stick insects.
View Article and Find Full Text PDFPhilos Trans R Soc Lond B Biol Sci
August 2020
Simpson's fossil-record inspired model of 'adaptive zones' proposes that evolution is dominated by small fluctuations within adaptive zones, occasionally punctuated by larger shifts between zones. This model can help explain why the process of population divergence often results in weak or moderate reproductive isolation (RI), rather than strong RI and distinct species. Applied to the speciation process, the adaptive zones hypothesis makes two inter-related predictions: (i) large shifts between zones are relatively rare, (ii) when large shifts do occur they generate stronger RI than shifts within zones.
View Article and Find Full Text PDFThe frequent occurrence of adaptive radiations on oceanic islands and in lakes is often attributed to ecological opportunity resulting from release from competition where arrival order among lineages predicts which lineage radiates. This occurs when the lineage that arrives first expands its niche breadth and diversifies into a set of ecological specialists with associated monopolization of the resources. Later-arriving species do not experience ecological opportunity and do not radiate.
View Article and Find Full Text PDFAdaptive radiations, in which repeated bouts of diversification lead to phenotypically similar species, highlight the power of natural selection and predictability in evolution. A newly discovered radiation of stick spiders on Hawaii helps shed new light on this phenomenon.
View Article and Find Full Text PDFSpeciation can involve a transition from a few genetic loci that are resistant to gene flow to genome-wide differentiation. However, only limited data exist concerning this transition and the factors promoting it. Here, we study phases of speciation using data from >100 populations of 11 species of Timema stick insects.
View Article and Find Full Text PDFThe cichlid family features some of the most spectacular examples of adaptive radiation. Evolutionary studies have highlighted the importance of both trophic adaptation and sexual selection in cichlid speciation. However, it is poorly understood what processes drive the composition and diversity of local cichlid species assemblages on relatively short, ecological timescales.
View Article and Find Full Text PDFAggressive mimicry is an adaptive tactic of parasitic or predatory species that closely resemble inoffensive models in order to increase fitness via predatory gains. Although similarity of distantly related species is often intuitively implicated with mimicry, the exact mechanisms and evolutionary causes remain elusive in many cases. Here, we report a complex aggressive mimicry strategy in Plecodus straeleni, a scale-eating cichlid fish from Lake Tanganyika, which imitates two other cichlid species.
View Article and Find Full Text PDFThe interplay between selection and aspects of the genetic architecture of traits (such as linkage, dominance, and epistasis) can either drive or constrain speciation [1-3]. Despite accumulating evidence that speciation can progress to "intermediate" stages-with populations evolving only partial reproductive isolation-studies describing selective mechanisms that impose constraints on speciation are more rare than those describing drivers. The stick insect Timema cristinae provides an example of a system in which partial reproductive isolation has evolved between populations adapted to different host plant environments, in part due to divergent selection acting on a pattern polymorphism [4, 5].
View Article and Find Full Text PDFAdaptive radiation (AR) is a key process in the origin of organismal diversity. However, the evolution of trait disparity in connection with ecological specialization is still poorly understood. Available models for vertebrate ARs predict that diversification occurs in the form of temporal stages driven by different selective forces.
View Article and Find Full Text PDFThe recurrent evolution of convergent forms is a widespread phenomenon in adaptive radiations (e.g., [1-9]).
View Article and Find Full Text PDFThe evolution of convergent phenotypes is one of the most interesting outcomes of replicate adaptive radiations. Remarkable cases of convergence involve the thick-lipped phenotype found across cichlid species flocks in the East African Great Lakes. Unlike most other convergent forms in cichlids, which are restricted to East Africa, the thick-lipped phenotype also occurs elsewhere, for example in the Central American Midas Cichlid assemblage.
View Article and Find Full Text PDFAntarctic notothenioid fishes represent a rare example of a marine species flock. They evolved special adaptations to the extreme environment of the Southern Ocean including antifreeze glycoproteins. Although lacking a swim bladder, notothenioids have diversified from their benthic ancestor into a wide array of water column niches, such as epibenthic, semipelagic, cryopelagic and pelagic habitats.
View Article and Find Full Text PDFBackground: Phenotypic evolution and its role in the diversification of organisms is a central topic in evolutionary biology. A neglected factor during the modern evolutionary synthesis, adaptive phenotypic plasticity, more recently attracted the attention of many evolutionary biologists and is now recognized as an important ingredient in both population persistence and diversification. The traits and directions in which an ancestral source population displays phenotypic plasticity might partly determine the trajectories in morphospace, which are accessible for an adaptive radiation, starting from the colonization of a novel environment.
View Article and Find Full Text PDFSympatric speciation, the formation of species in the absence of geographical barriers, remains one of the most contentious concepts in evolutionary biology. Although speciation under sympatric conditions seems theoretically possible, empirical studies are scarce and only a few credible examples of sympatric speciation exist. Here we present a convincing case of sympatric speciation in the Midas cichlid species complex (Amphilophus sp.
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