Colonization Of Novel Habitats Research Articles

Life form evolution in epidendroid orchids: Ecological consequences of the shift from epiphytism to terrestrial habit in Hexalectris

AbstractGreat diversity of life forms has favored the colonization and dominance of angiosperms in almost every terrestrial habitat. This is certainly the case in the Orchidaceae, in which the diversity of life forms includes epiphytes, terrestrial geophytes and mycoheterotrophs. In this study we investigated the evolution of life form in tribe Epidendreae focusing on the clade comprised of Basiphyllaea, Bletia and Hexalectris. We estimated divergence dates, ancestral areas, patterns of niche evolution and divergence/convergence of climate preferences in order to understand whether shifts in climate preferences can be linked to the evolution of novel life forms, allowing species to extend their distribution ranges into novel habitats. Our analyses corroborated the shift from epiphytism to terrestrial life forms in Epidendreae, which occurred in a clade with Basiphyllaea‐Bletia‐Hexalectris that originated in Mexico and Central America from the Mid‐Eocene to the Oligocene, coincident with the origin of other aridity‐adapted plant groups. Dispersal occurred to North America, South America and the Antilles. Some small aridity‐adapted groups in Hexalectris diverged more recently in the Pliocene and Pleistocene when aridification in North America occurred. Of the climate variables analyzed, annual mean temperature, annual precipitation and precipitation of the wettest month were found to diverge for the terrestrial clade relative to values associated with the other Epidendreae clades. For niche evolution, Ornstein‐Uhlenbeck models indicated that the adaptive optima differed between epiphytes and terrestrial life forms, suggesting a shift of climatic niche between the terrestrial life form clade of Basiphyllaea‐Bletia‐Hexalectris and the rest of the clades with epiphyte life forms. We suggest that the shift to terrestrial life forms, most noticeable in Hexalectris, favored the colonization of novel habitats with a large range of temperatures, extending the distribution of this genus northward.

Plasticity in social communication and its implications for the colonization of novel habitats

Puerto Rican lizards tailor the performance of elaborate headbob displays to ensure rivals “get the message” in most viewing conditions. This capability (or plasticity) means that most territorial lizards should be able to maintain an effective communication system in a range of habitats. This has important implications for our understanding of how social animals cope when they move to a novel environment or when there are major changes in viewing conditions in a current habitat.

On the prospect of identifying adaptive loci in recently bottlenecked populations.

Identifying adaptively important loci in recently bottlenecked populations – be it natural selection acting on a population following the colonization of novel habitats in the wild, or artificial selection during the domestication of a breed – remains a major challenge. Here we report the results of a simulation study examining the performance of available population-genetic tools for identifying genomic regions under selection. To illustrate our findings, we examined the interplay between selection and demography in two species of Peromyscus mice, for which we have independent evidence of selection acting on phenotype as well as functional evidence identifying the underlying genotype. With this unusual information, we tested whether population-genetic-based approaches could have been utilized to identify the adaptive locus. Contrary to published claims, we conclude that the use of the background site frequency spectrum as a null model is largely ineffective in bottlenecked populations. Results are quantified both for site frequency spectrum and linkage disequilibrium-based predictions, and are found to hold true across a large parameter space that encompasses many species and populations currently under study. These results suggest that the genomic footprint left by selection on both new and standing variation in strongly bottlenecked populations will be difficult, if not impossible, to find using current approaches.

Renewed diversification is associated with new ecological opportunity in theNeotropical turtle ants

Ecological opportunity, defined as access to new resources free from competitors, is thought to be a catalyst for the process of adaptive radiation. Much of what we know about ecological opportunity, and the larger process of adaptive radiation, is derived from vertebrate diversification on islands. Here, we examine lineage diversification in the turtle ants (Cephalotes), a species-rich group of ants that has diversified throughout the Neotropics. We show that crown group turtle ants originated during the Eocene (around 46 mya), coincident with global warming and the origin of many other clades. We also show a marked lineage-wide slowdown in diversification rates in the Miocene. Contrasting this overall pattern, a species group associated with the young and seasonally harsh Chacoan biogeographic region underwent a recent burst of diversification. Subsequent analyses also indicated that there is significant phylogenetic clustering within the Chacoan region and that speciation rates are highest there. Together, these findings suggest that recent ecological opportunity, from successful colonization of novel habitat, may have facilitated renewed turtle ant diversification. Our findings highlight a central role of ecological opportunity within a successful continental radiation.

Do habitat shifts drive diversification in teleost fishes? An example from the pufferfishes (Tetraodontidae)

Habitat shifts are implicated as the cause of many vertebrate radiations, yet relatively few empirical studies quantify patterns of diversification following colonization of new habitats in fishes. The pufferfishes (family Tetraodon-tidae) occur in several habitats, including coral reefs and freshwater, which are thought to provide ecological opportunity for adaptive radiation, and thus provide a unique system for testing the hypothesis that shifts to new habitats alter diversification rates. To test this hypothesis, we sequenced eight genes for 96 species of pufferfishes and closely related porcupine fishes, and added 19 species from sequences available in GenBank. We time-calibrated the molecular phylogeny using three fossils, and performed several comparative analyses to test whether colonization of novel habitats led to shifts in the rate of speciation and body size evolution, central predictions of clades experiencing ecological adaptive radiation. Colonization of freshwater is associated with lower rates of cladogenesis in pufferfishes, although these lineages also exhibit accelerated rates of body size evolution. Increased rates of cladogenesis are associated with transitions to coral reefs, but reef lineages surprisingly exhibit significantly lower rates of body size evolution. These results suggest that ecological opportunity afforded by novel habitats may be limited for pufferfishes due to competition with other species, constraints relating to pufferfish life history and trophic ecology, and other factors.

Inbreeding depression and partitioning of genetic load in the invasive biennial Alliaria petiolata (Brassicaceae)

Invasive species are nonnative species that enter novel environments, establish sustained populations, and can negatively impact native species. Here we assess a potential weakness of invasive species (genetic load) and show how species might overcome genetic barriers. Colonization of novel habitats by invasive species typically involves few individuals, exposing populations to founder effects. We empirically tested a central Illinois population of an invasive biennial plant, Alliaria petiolata, for evidence of a founder effect by assessing the pattern of genetic load. • To estimate genetic load, we assayed offspring from three cross types (self-pollinated, outcrossed within- and between-populations) in a greenhouse. Vegetative and reproductive traits were measured on first-year plants grown with or without intraspecific competition. • We found substantial genetic load in this population of A. petiolata, which can mostly be attributed to genetic drift (founder effect) and not inbreeding depression. Between-population heterosis was expressed more than inbreeding depression under intraspecific competition. • Inbreeding may be adaptive for A. petiolata in its introduced range by providing reproductive assurance, with limited inbreeding load. Nevertheless, most of the genetic load in this population of A. petiolata is due to fixation of deleterious alleles. Drift load is expected, given that this population is near the edge of its continuous geographic range in highly fragmented habitats, and gene flow between isolated populations is likely highly limited. Preventing additional introduction and movement of propagules between isolated local populations should reduce heterosis and A. petiolata competitiveness.

The interaction between propagule pressure, habitat suitability and density‐dependent reproduction in species invasion

Seedling recruitment limitations create a demographic bottleneck that largely determines the viability and structure of plant populations and communities, and pose a core restriction on the colonization of novel habitat. We use a shade‐tolerant, invasive grass, Microstegium vimineum, to examine the interplay between seed and establishment limitations – phenomena that together determine recruitment success but usually are investigated individually. We add increasing amounts of seed to microhabitats containing variable levels of leaf litter thickness – with reduced leaf litter simulating disturbance – to investigate whether reduced seed limitation overcomes the establishment limitation posed by litter cover. We do this across gradients in understory light, moisture and temperature, and quantify germination, survival, and then per capita adult biomass and reproduction in order to understand the implications for invasion across the landscape. We find that the combined effects of seed and establishment limitation influence recruitment; however, propagule pressure overwhelms the inhibitory effects of leaf litter thickness. Leaf litter reduces germination by 22–57% and seedling survival by 13–15% from that observed on bare soil. However, density‐dependent reproduction compensates as 1–3 plants can produce far more seeds (approx. 525) than are required for persistence. As such, just a few plants may establish in understory forest habitat and subsequently overwhelm establishment barriers with copious propagule production. These results, for a widespread, invasive plant, are consistent with the emerging perspective for native plants that seed and establishment limitation jointly influence recruitment. The ability for an exotic plant species to compensate for low population densities with high per capita seed production, that then overrides establishment limitations, makes its invasive potential daunting. Further work is required to test if this is a common mechanism underlying plant invasions.

Colonization of novel White Sands habitat is associated with changes in lizard anti-predator behaviour

Colonization of novel habitats is often associated with differences in ecological community composition. For small diurnal animals, differences in predator diversity and abundance can lead to behavioural shifts in the novel habitat. The eastern fence lizard Sceloporus undulatus (Bosc and Daudin, 1801) recently colonized the gypsum dunes of White Sands, a predator-poor community relative to the predator-rich community of the surrounding Chihuahuan dark-soil habitat. We used field experiments to assess S. undulatus anti-predator behaviour in white-sand versus dark-soil habitats, and used laboratory assays to determine whether behavioural differences could be mediated by hormonal regulation. Overall, we found that white-sand lizards were less vigilant but more wary than their dark-soil counterparts; it took them longer to detect a simulated predator, but once detected they were more likely to retreat from their perches than dark-soil lizards. At the proximate level, differences in anti-predator behaviour could not be explained by differences in plasma hormone levels (corticosterone and testosterone); we detected elevated corticosterone for lizards in our stress treatment relative to control treatment, but found no differences between habitats in baseline or acute corticosterone levels. At the evolutionary level, we suggest that differences in anti-predator behaviour may be explained by differences across habitats in predation environment, habituation, and/or the cost of retreating. Our study implicates changes in predator community composition in mediating ecological divergence in behaviour.

Molecular and morphological divergence in the inland silverside (Menidia beryllina) along a freshwater-estuarine interface

Populations that vary across ecological gradients or that have invaded novel habitats are important to elucidate the association between adaptive divergence and gene flow, factors that may play an important role in speciation of silverside fishes. The inland silverside, Menidia beryllina, is an ideal organism for this kind of research, displaying a great diversity in morphology among freshwater and coastal brackish habitats. Using a combination of geometric morphometrics and mitochondrial (mt) DNA, we investigated patterns of variation within and among the nominal freshwater Menidia audens and coastal M. beryllina, spanning the transition from freshwater to tidally influenced semi-brackish waters of the lower Mississippi River to brackish waters of the Lake Pontchartrain estuary. Although we found no evidence for a phylogenetic split between M. audens and M. beryllina, our results indicate that significant genetic divergence corresponds with body shape differences among the two, with a clear distinction at the interface of freshwater and brackish water. Patterns in mtDNA suggest that freshwater populations referred to as M. audens are of recent origin with evidence for habitat-based divergence compared to coastal populations referred to as M. beryllina. Our findings add to a growing body of evidence that ecological shifts, following colonization of novel habitats, may promote rapid adaptive divergence and reduced gene flow among silverside populations in adjacent environmental regimes.

Natural functions of lipopeptides fromBacillusandPseudomonas: more than surfactants and antibiotics

Lipopeptides constitute a structurally diverse group of metabolites produced by various bacterial and fungal genera. In the past decades, research on lipopeptides has been fueled by their antimicrobial, antitumour, immunosuppressant and surfactant activities. However, the natural functions of lipopeptides in the lifestyles of the producing microorganisms have received considerably less attention. The substantial structural diversity of lipopeptides suggests that these metabolites have different natural roles, some of which may be unique to the biology of the producing organism. This review gives a detailed overview of the versatile functions of lipopeptides in the biology of Pseudomonas and Bacillus species, and highlights their role in competitive interactions with coexisting organisms, including bacteria, fungi, oomycetes, protozoa, nematodes and plants. Their functions in cell motility, leading to colonization of novel habitats, and in the formation and development of highly structured biofilms are discussed in detail. Finally, this review provides an update on lipopeptide detection and discovery as well as on novel regulatory mechanisms and genes involved in lipopeptide biosynthesis in these two bacterial genera.

A MULTILOCUS PERSPECTIVE ON COLONIZATION ACCOMPANIED BY SELECTION AND GENE FLOW

The colonization of novel habitats involves complex interactions between founder events, selection, and ongoing migration, and can lead to diverse evolutionary outcomes from local extinction to adaptation to speciation. Although there have been several studies of the demography of colonization of remote habitats, less is known about the demographic consequences of colonization of novel habitats within a continuous species range. Populations of the Eastern Fence Lizard, Sceloporus undulatus, are continuously distributed across two dramatic transitions in substrate color in southern New Mexico and have undergone rapid adaptation following colonization of these novel environments. Blanched forms inhabit the gypsum sand dunes of White Sands and melanic forms are found on the black basalt rocks of the Carrizozo lava flow. Each of these habitats formed within the last 10,000 years, allowing comparison of genetic signatures of population history for two independent colonizations from the same source population. We present evidence on phenotypic variation in lizard color, environmental variation in substrate color, and sequence variation for mitochondrial DNA and 19 independent nuclear loci. To confirm the influence of natural selection and gene flow in this system, we show that phenotypic variation is best explained by environmental variation and that neutral genetic variation is related to distance between populations, not partitioned by habitat. The historical demography of colonization was inferred using an Approximate Bayesian Computation (ABC) framework that incorporates known geological information and allows for ongoing migration with the source population. The inferences differed somewhat between mtDNA and nuclear markers, but overall provided strong evidence of historical size reductions in both white sand and black lava populations at the time of colonization. Populations in both novel habitats appear to have undergone partial but incomplete recovery from the initial bottleneck. Both ABC analyses and measures of mtDNA sequence diversity also suggested that population reductions were more severe in the black lava compared to the white sands habitat. Differences observed between habitats may be explained by differences in colonization time, habitat geometry, and strength or response to natural selection for substrate matching. Finally, effective population size reductions in this system appear to be more dramatic when colonization is accompanied by a change in selection regime. Our analyses are consistent with a demographic cost of adaptation to novel environments and show that it is possible to infer aspects of the historical demography of local adaptation even in the presence of ongoing gene flow.

Colonization of novel habitat: Tests of generality of patterns in a diverse invertebrate assemblage

Understanding colonization and use of novel habitat by diverse assemblages is increasingly important as natural habitats are disturbed or replaced. How well novel habitats will be used by biota depends on (i) how well they mimic natural habitat and (ii) how adaptable are the fauna in utilizing different types of habitat. Much of our understanding of colonization of patchy habitats is derived from studies in which colonizing fauna respond strongly to biotic stimuli. Comparisons of patterns of colonization among patches, across landscapes, over time, etc., may thus be confounded by differences in the quality of the patches themselves, which may interact with other features of the broader landscape. Intertidal boulder-fields have many features that make them ideal for extending studies of colonization by diverse assemblages because the organisms living on boulders live in naturally patchy habitats, separated by a matrix which is differentially permeable to different components of this biota. This study used standardized, novel patches of habitat as surrogates of natural boulders in order to control the physical features of these patches. These units of habitat resemble quarried rock that is frequently added to nearshore environments in the form of groynes or breakwaters, or which is commonly disposed of in urbanized estuaries. Previous work has shown that they are readily colonized and used by a similar range of taxa as are natural boulders. Here, they were added to existing boulder-fields to test specific hypotheses regarding colonization of different types of patches across replicate sites, times, periods of deployment and levels of taxonomic grouping. All tests showed extremely variable colonization, with little support for more deterministic models that have been proposed to explain species–habitat relationships. Variability in colonization mimicked natural levels of variability in these fauna reported elsewhere. Colonization of novel habitats in this system seems therefore to be strongly influenced by stochastic variation in supply of colonists and their ability of colonists to utilize and move through he surrounding matrix, rather than on the quality of habitat itself. This needs careful consideration in attempts to manage or repair damaged marine habitats.

Revisiting evolutionary dead ends in sockeye salmon (Oncorhynchus nerka) life history

This study challenges recent hypotheses about sockeye salmon (Oncorhynchus nerka) colonization based on life history and broadens the pathways that investigators should consider when studying sockeye colonization of novel habitats. Most sockeye populations exhibit lake-type life histories. Riverine populations are thought to be more likely to stray from their natal stream to spawn and therefore colonize new habitat. We examined genetic relationships among five geographically proximate sockeye populations from the Aniakchak region of the Alaska Peninsula, Alaska. Specifically, we sought to determine if the genetic population structure was consistent with the hypothesis that a riverine population colonized a recently available upriver volcanic caldera lake, and whether recent volcanism led to genetic bottlenecks in these sockeye populations. Heterozygosity and allelic richness were not higher in the riverine population. Patterns of genetic divergence suggested that the geographically proximate riverine sockeye population did not colonize the lake; the caldera populations were more genetically divergent from the downstream riverine population (FST = 0.047) than a lake-type population in a different drainage (FST = 0.018). Our results did not suggest the presence of genetic bottlenecks in the caldera populations.

Hybridization and the colonization of novel habitats by annual sunflowers

Although invasive plant species often have a hybrid ancestry, unambiguous evidence that hybridization has stimulated the evolution of invasive behaviors has been difficult to come by. Here, we briefly review how hybridization might contribute to the colonization of novel habitats, range expansions, and invasiveness and then describe work on hybrid sunflowers that forges a direct link between hybridization and ecological divergence. We first discuss the invasion of Texas by the common sunflower and show that the introgression of chromosomal segments from a locally adapted species may have facilitated range expansion. We then present evidence that the colonization of sand dune, desert floor, and salt marsh habitats by three hybrid sunflower species was made possible by selection on extreme or "transgressive" phenotypes generated by hybridization. This body of work corroborates earlier claims regarding the role of hybridization in adaptive evolution and provides an experimental and conceptual framework for ongoing studies in this area.