Key Ecological Traits Research Articles

Shifting microbial communities in acidified seawaters: insights from polychaetes living in the CO2 vent of Ischia, Italy.

Oceans' absorption of human-related CO2 emissions leads to a process called ocean acidification (OA), consisting of the decrease of the seawater pH with negative consequences for many marine organisms. In this study, we investigate the microbial community of two species of polychaetes found in naturally acidified CO2 vents: the nereid Platynereis massiliensis complex and the syllid Syllis prolifera. Animals were collected in the CO2 vents of Castello Aragonese (Gulf of Naples, Ischia, Italy) in three zones at decreasing pH. For the analysis of the microbiome, the V3-V4 hypervariable region of the 16S ribosomal RNA gene of 40 worm samples was sequenced on an Illumina MiSeq platform. No difference in the microbial alpha diversity of both species was highlighted. On the contrary, the microbial composition of worms collected in the site at normal pH was different from that of the individuals obtained from the sites at lower pH. This effect was evident also in samples from the site with a slight, but relevant, degree of acidification. Amplicon sequence variants showing a significant variation among the groups of samples collected from different pH zones were reported for both polychaetes, but no common trend of variation was observed. The present study deepens our knowledge about the composition of polychaete microbiome in marine naturally acidified sites. Our results stress the importance of future investigations about the connection between the variation of environmental and polychaete microbial communities induced by OA and about the effect of these variations on polychaete key biological and ecological traits.

Social selection analysis reveals limited effect of neighbors' traits in Tree swallows.

Social interactions are ubiquitous in nature and can shape the fitness of individuals through social selection. This type of selection arises when phenotypes of neighbors influence the fitness of a focal individual. Quantifying social selection is crucial to better characterize the overall selective landscape. For example, if intraspecific competition is strong, traits that are beneficial for an individual could be detrimental to competitors. In this study, we quantified social selection acting on three key ecological traits (body mass, wing length, and laying date) in wild Tree swallow (Tachycineta bicolor) females. We used reproductive success measured at three stages throughout the breeding season as fitness proxies to assess selection acting at those decisive moments. We also quantified the effects of environment on selection using measures of conspecifics' density, type of agricultural landscape, and presence of interspecific competitors. Overall, we found no strong evidence of social selection on these traits in our study system, although there were marginally nonsignificant selection gradients suggesting the positive effect of larger neighbors. Environmental variables affected reproductive success but did not strongly affect social selection gradients. Our study calls for more social selection estimates to be reported across environments to better understand its importance in wild populations.

Species traits to guide moth conservation in anthropogenic regions: A multi‐species approach using distribution trends in Flanders (northern Belgium)

Abstract Insect abundance and diversity appear to decline rapidly in recent decades, garnering significant media attention, and hence raising public awareness. Macro‐moths—a species‐rich and ecologically diverse insect group—face severe declines, particularly in urbanised and intensively farmed areas in NW Europe. Flanders is a highly anthropogenic region, serving as a case study where the impact on macro‐moths of stressors like intensive agriculture, industrialisation and urbanisation has been quantified through a recently compiled Red List. Here, for 717 macro‐moth species, we calculated relative changes in distribution area between a reference period (1980–2012) and the subsequent period (2013–2022). By correlating these species‐specific trends with 10 key ecological and life history traits, we calculated more general Multi‐Species Change Indices (MSCIs). These MSCIs showed that species associated with wet biotopes and heathlands declined on average by 20%–25%, while (sub)urban species increased by more than 60%. Species feeding on lichens or mosses increased by 31%, while grass‐feeding species decreased by 20%. Both very small (+34%) and very large species (+15%) increased, whereas medium‐sized species decreased by 5%. Monophagous (+17%), migrant (+88%) and colour‐invariable species (+5%) increased, while colour‐variable species decreased (−8%). Finally, Holarctic (−21%) and Palaearctic species (−5%) decreased, while Mediterranean (+27%) and Western‐Palaearctic species (+9%) increased. Our trait‐based approach identifies key threats and mitigation strategies for moths in anthropogenic regions, offering evidence‐based insights for crafting efficient management recommendations and informed conservation policies to safeguard moth communities.

Promotion of seedling germination in Arabidopsis by B-box zinc-finger protein BBX32

Seed germination represents a determinant for plants to enter ecosystems and is thus regarded as a key ecological and agronomic trait. It is tightly regulated by a variety of environmental cues to ensure that seeds germinate under favorable conditions. Here, we characterize BBX32, a B-box zinc-finger protein, as an imbibition-stimulated positive regulator of seed germination. Belonging to subgroup V of the BBX family, BBX32 exhibits distinct characteristics compared with its close counterparts within the same subgroup. BBX32 is transiently induced at both the transcriptional and post-transcriptional levels in the embryo upon water absorption. Genetic evidence indicates that BBX32 acts upstream of the master transcription factor PHYTOCHROME-INTERACTING FACTOR 1 (PIF1) to facilitate light-induced seed germination. BBX32 directly interacts with PIF1, suppressing its protein-interacting and DNA-binding capabilities, thereby relieving PIF1's repression on seed germination. Furthermore, the imbibition-stimulated BBX32 functions in parallel with the light-induced transcription regulator HFR1 to collectively attenuate the transcriptional activities of PIF1. The BBX32-PIF1 de-repression module serves as a molecular connection that enables plants to integrate signals of water availability and light exposure, effectively coordinating the initiation of seed germination.

Smaller microorganisms outcompete larger ones in resistance and functional effects under disturbed agricultural ecosystems.

Body size is a key ecological trait of soil microorganisms related to their adaptation to environmental changes. In this study, we reveal that the smaller microorganisms show stronger community resistance than larger organisms in both maize and rice soil. Compared with larger organisms, smaller microorganisms have higher diversity and broader niche breadth to deploy survival strategies, because of which they are less affected by environmental selection and thus survive in complex and various kinds of environments. In addition, the strong correlation between smaller microorganisms and ecosystem functions reflects their greater metabolic flexibility and illustrates their significant roles in adaptation to continuously changing environments. This research highlights the importance of body size in maintaining stability of the soil microbiome and forecasting agroecosystem dynamics under environmental disturbances.

Differentiation in Leaf Functional Traits and Driving Factors of the Allopatric Distribution of Tetraploid and Octaploid Buddleja macrostachya in the Sino-Himalayan Region

Leaf functional traits reflect species’ adaptive strategies and habitat requirements. Examining intra-specific variations and their underlying drivers can aid in comprehending species differentiation and adaptation. Here, we investigated the leaf functional traits of Buddleja macrostachya tetraploids and octaploids across 18 sites in the Sino-Himalayan region. The habitat environmental variables were also recorded. In this study, leaf functional traits showed a considerable differentiation in both tetraploid and octaploid B. macrostachya. Redundancy analysis (RDA) revealed that the octaploid cytotypes displayed higher specific leaf area, leaf total nitrogen and phosphorus concentrations, water-use efficiency, and light-use efficiency in contrast to the tetraploid plants. These functional leaf traits exhibited different plasticity levels in both taxa. A positive link was found between habitat altitude and soil total P concentration and the geographic distribution of the B. macrostachya complex, using RDA and Pearson’s correlation. Our findings suggest that both tetraploid and octaploid B. macrostachya exhibited divergent ecological strategies, conservative and acquisitive strategies, respectively. The ecological adaptability of species within the B. macrostachya complex is enhanced by the combination of divergent ecological strategies and high phenotypic plasticity of distinct key ecological traits. Furthermore, abiotic environmental factors influenced the allopatric geographic distribution pattern of the B. macrostachya complex in the Sino-Himalayan region.

Metabolic plasticity drives mismatches in physiological traits between prey and predator

Metabolic rate, the rate of energy use, underpins key ecological traits of organisms, from development and locomotion to interaction rates between individuals. In a warming world, the temperature-dependence of metabolic rate is anticipated to shift predator-prey dynamics. Yet, there is little real-world evidence on the effects of warming on trophic interactions. We measured the respiration rates of aquatic larvae of three insect species from populations experiencing a natural temperature gradient in a large-scale mesocosm experiment. Using a mechanistic model we predicted the effects of warming on these taxa’s predator-prey interaction rates. We found that species-specific differences in metabolic plasticity lead to mismatches in the temperature-dependence of their relative velocities, resulting in altered predator-prey interaction rates. This study underscores the role of metabolic plasticity at the species level in modifying trophic interactions and proposes a mechanistic modelling approach that allows an efficient, high-throughput estimation of climate change threats across species pairs.

Extending Grime's CSR model to predict plant demographic responses across resource availability gradients: evidence from the patagonian steppes

Sexual reproduction, growth, and survival are crucial demographic strategies for plant population viability. Here, we propose a conceptual model predicting demographic responses of species based on their ecological strategy and the heterogeneity of environmental conditions within a biogeographical unit and then applied it to a case study from a 5˚ latitudinal gradient in the Patagonian steppes. We also aim to disentangle genetic from environmental effects on demographic responses. We performed in situ and common garden experiments with two species from six local populations of the Occidental Phytogeographical District of the Patagonian steppes. Species differ in key ecological traits, and thus fit into Grime's model for evolutionary strategies in plants: one as competitive species and the other as stress‐tolerant species. We calculated population growth rate (λ) and performed elasticity analyses to compare the contribution of each demographic strategy to population fitness between species and among local populations distributed along 600 km latitudinal gradient with differences in mean annual precipitation (MAP). We highlight four results. First, the competitive species change from sexual reproduction to growth as MAP increases. Second, the stress‐tolerant species relied on growth and survival along the MAP gradient. Third, interannual variation in resource availability modulated demographic responses for both strategies. Fourth, based on the comparison of the in situ and common garden experiments, we submit that demographic responses were genetically driven. Our study shows that demographic responses can be roughly predicted by the ecological strategy across environmental gradients. We show that differences arise not only between species, but also were genetically driven differences within species among local populations. Scaling up plant‐level responses to population‐level dynamics allows for a process‐based understanding of current and future biogeographical species organization. Furthermore, conservation and restoration efforts should be guided by demographic strategies underlying population viability.

When Do Traits Tell More Than Species about a Metacommunity? A Synthesis across Ecosystems and Scales.

AbstractLinking species traits with the variation in species assemblages across habitats has often proved useful for developing a more mechanistic understanding of species distributions in metacommunities. However, summarizing the rich tapestry of a species in all of its nuance with a few key ecological traits can also lead to an abstraction that provides less predictability than when using taxonomy alone. As a further complication, taxonomic and functional diversities can be inequitably compared, either by integrating taxonomic-level information into the calculation of how functional aspects of communities vary or by detecting spurious trait-environment relationships. To remedy this, we here synthesize analyses of 80 datasets on different taxa, ecosystems, and spatial scales that include information on abundance or presence/absence of species across sites with variable environmental conditions and the species' traits. By developing analyses that treat functional and taxonomic diversity equitably, we ask when functional diversity helps to explain metacommunity structure. We found that patterns of functional diversity explained metacommunity structure and response to environmental variation in only 25% of the datasets using a multitrait approach but up to 59% using a single-trait approach. Nevertheless, an average of only 19% (interquartile range = 0%-29%) of the traits showed a significant signal across environmental gradients. Species-level traits, as typically collected and analyzed through functional diversity patterns, often do not bring predictive advantages over what the taxonomic information already holds. While our assessment of a limited advantage of using traits to explain variation in species assemblages was largely true across ecosystems, traits played a more useful role in explaining variation when many traits were used and when trait constructs were more related to species' status, life history, and mobility. We propose future research directions to make trait-based approaches and data more helpful for inference in metacommunity ecology.

Community-wide genome sequencing reveals 30 years of Darwin's finch evolution.

A fundamental goal in evolutionary biology is to understand the genetic architecture of adaptive traits. Using whole-genome data of 3955 of Darwin's finches on the Galápagos Island of Daphne Major, we identified six loci of large effect that explain 45% of the variation in the highly heritable beak size of Geospiza fortis, a key ecological trait. The major locus is a supergene comprising four genes. Abrupt changes in allele frequencies at the loci accompanied a strong change in beak size caused by natural selection during a drought. A gradual change in Geospiza scandens occurred across 30 years as a result of introgressive hybridization with G. fortis. This study shows how a few loci with large effect on a fitness-related trait contribute to the genetic potential for rapid adaptive radiation.

Global analysis of reef ecosystem services reveals synergies, trade-offs and bundles

Millions of people around the world depend on the ecosystem services produced by rocky and coral reef ecosystems, including nutrition, aesthetic value, and coastal protection. Rocky and coral reefs also contribute to critical global and regional processes through the cycling of nitrogen, phosphorus, and carbon. The increased stress experienced by reefs in the Anthropocene threatens their ability to provide vital ecosystem services. This study investigates bundles of ecosystem services, ecosystem services that occur together, to identify trade-offs and synergies among services produced by coral reefs. To do this, we bring together estimates of seven ecosystem services: productivity, nitrogen cycling, phosphorus cycling, inorganic carbon cycling, aesthetic value, nutritional value, and coastal protection. We use correlations analysis to understand trade-offs and synergies between these seven ecosystem services and cluster analysis to identify clusters of reefs with distinct suites of ecosystem services, or ecosystem service bundles. Our analysis reveals (1) synergies and trade-offs among the seven ecosystem services, and (2) three distinct clusters of reefs, which differ on the basis of their overall and relative delivery of ecosystem services. Differences in service production among the clusters appear to be linked to differences in key ecological traits, including total reef fish biomass and species richness. Similar applications of ecosystem service bundles analysis in other marine and coastal systems could result in improved understanding of the spatial distributions and relationships between marine ecosystem services, which is a key input to marine policy.

Colony size buffers interactions between neonicotinoid exposure and cold stress in bumblebees.

Social bees are critical for supporting biodiversity, ecosystem function and crop yields globally. Colony size is a key ecological trait predicted to drive sensitivity to environmental stressors and may be especially important for species with annual cycles of sociality, such as bumblebees. However, there is limited empirical evidence assessing the effect of colony size on sensitivity to environmental stressors or the mechanisms underlying these effects. Here, we examine the relationship between colony size and sensitivity to environmental stressors in bumblebees. We exposed colonies at different developmental stages briefly (2 days) to a common neonicotinoid (imidacloprid) and cold stress, while quantifying behaviour of individuals. Combined imidacloprid and cold exposure had stronger effects on both thermoregulatory behaviour and long-term colony growth in small colonies. We find that imidacloprid's effects on behaviour are mediated by body temperature and spatial location within the nest, suggesting that social thermoregulation provides a buffering effect in large colonies. Finally, we demonstrate qualitatively similar effects in size-manipulated microcolonies, suggesting that group size per se, rather than colony age, drives these patterns. Our results provide evidence that colony size is critical in driving sensitivity to stressors and may help elucidate mechanisms underlying the complex and context-specific impacts of pesticide exposure.

Evolution of nest architecture in tyrant flycatchers and allies.

Innovations in nest design are thought to be one potential factor in the evolutionary success of passerine birds (order: Passeriformes), which colonized new ecological niches as they diversified in the Oligocene and Miocene. In particular, tyrant flycatchers and their allies (parvorder: Tyrannida) are an extremely diverse group of New World suboscine passerines occupying a wide range of habitats and exhibiting substantial extant variation in nest design. To explore the evolution of nest architecture in this clade, we first described nest traits across the Tyrannida phylogeny and estimated ancestral nest conditions. We then quantified macroevolutionary transition rates between nest types, examined a potential coevolutionary relationship between nest type and habitat, and used phylogenetic mixed models to determine possible ecological and environmental correlates of nest design. The Tyrannida ancestor probably built a cup nest in a closed habitat, and dome nests independently evolved at least 15 times within this group. Both cup- and dome-nesting species diversified into semi-open and open habitats, and we did not detect a coevolutionary relationship between nest type and habitat. Furthermore, nest type was not significantly correlated with several key ecological, life-history and environmental traits, suggesting that broad variation in Tyrannida nest architecture may not easily be explained by a single factor. This article is part of the theme issue 'The evolutionary ecology of nests: a cross-taxon approach'.

Melanization slows the rapid movement of fungal necromass carbon and nitrogen into both bacterial and fungal decomposer communities and soils.

Microbial necromass contributes significantly to both soil carbon (C) persistence and ecosystem nitrogen (N) availability, but quantitative estimates of C and N movement from necromass into soils and decomposer communities are lacking. Additionally, while melanin is known to slow fungal necromass decomposition, how it influences microbial C and N acquisition as well as elemental release into soils remains unclear. Here, we tracked decomposition of isotopically labeled low and high melanin fungal necromass and measured 13C and 15N accumulation in surrounding soils and microbial communities over 77 d in a temperate forest in Minnesota, USA. Mass loss was significantly higher from low melanin necromass, corresponding with greater 13C and 15N soil inputs. A taxonomically and functionally diverse array of bacteria and fungi was enriched in 13C and/or 15N at all sampling points, with enrichment being consistently higher on low melanin necromass and earlier in decomposition. Similar patterns of preferential C and N enrichment of many bacterial and fungal genera early in decomposition suggest that both microbial groups co-contribute to the rapid assimilation of resource-rich soil organic matter inputs. While overall richness of taxa enriched in C was higher than in N for both bacteria and fungi, there was a significant positive relationship between C and N in co-enriched taxa. Collectively, our results demonstrate that melanization acts as a key ecological trait mediating not only fungal necromass decomposition rate but also necromass C and N release and that both elements are rapidly co-utilized by diverse bacterial and fungal decomposers in natural settings. IMPORTANCE Recent studies indicate that microbial dead cells, particularly those of fungi, play an important role in long-term carbon persistence in soils. Despite this growing recognition, how the resources within dead fungal cells (also known as fungal necromass) move into decomposer communities and soils are poorly quantified, particularly in studies based in natural environments. In this study, we found that the contribution of fungal necromass to soil carbon and nitrogen availability was slowed by the amount of melanin present in fungal cell walls. Further, despite the overall rapid acquisition of carbon and nitrogen from necromass by a diverse range of both bacteria and fungi, melanization also slowed microbial uptake of both elements. Collectively, our results indicate that melanization acts as a key ecological trait mediating not only fungal necromass decomposition rate, but also necromass carbon and nitrogen release into soil as well as microbial resource acquisition.

The role of cell size in shaping responses to oxygen and temperature in fruit flies

Abstract The body size of an animal is strongly coupled to key ecological traits such as fecundity, mortality and growth. Ectothermic animals mature at smaller body sizes in warmer conditions and under low oxygen availability (hypoxia). Whether these responses result from changes in cell size and cell number (which together determine body size) and how such cellular responses may help ectotherms cope with heat and hypoxia is poorly understood. The theory of optimal cell size postulates that cell size imposes constraints on oxygen delivery: Differences in cell size result in differences in membrane surface‐to‐volume ratio, which impact the capacity of cells to take up oxygen and has consequences for growth rate and hence body size. Here, using inbred lines of fruit flies Drosophila melanogaster, which exhibit differences in cell size, we demonstrate that thermal responses in body size are magnified under hypoxia and in lines of flies that exhibit larger cell size. Furthermore, reductions in body size were partly manifested via reductions in cell size, resulting in a coupling between the body mass and cell size of flies. The coupling between cell size and body size was tighter under conditions where oxygen is expected to become limited, that is, warm or hypoxia, supporting the idea that capacity for oxygen uptake is causally related to organismal growth and the resulting body size. Our data indicate that the benefits of diffusive oxygen uptake due to the higher surface‐to‐volume ratios in smaller cells can help explain the temperature‐size rule in this species. Read the free Plain Language Summary for this article on the Journal blog.

Prevalent introgression underlies convergent evolution in the diversification of Pungitius sticklebacks.

New mutations and standing genetic variations contribute significantly to repeated phenotypic evolution in sticklebacks. However, less is known about the role of introgression in this process. We analysed taxonomically and geographically comprehensive genomic data from Pungitius sticklebacks to decipher the extent of introgression and its consequences for the diversification of this genus. Our results demonstrate that introgression is more prevalent than suggested by earlier studies. Although gene flow was generally bidirectional, it was often asymmetric and left unequal genomic signatures in hybridizing species, which might, at least partly, be due to biased hybridization and/or population size differences. In several cases, introgression of variants from one species to another was accompanied by transitions of pelvic and/or lateral plate structures - important diagnostic traits in Pungitius systematics - and frequently left signatures of adaptation in the core gene regulatory networks of armor trait development. This finding suggests that introgression has been an important source of genetic variation and enabled phenotypic convergence among Pungitius sticklebacks. The results highlight the importance of introgression of genetic variation as a source of adaptive variation underlying key ecological and taxonomic traits. Taken together, our study indicates that introgression-driven convergence likely explains the longstanding challenges in resolving the taxonomy and systematics of this small but phenotypically highly diverse group of fish.

Birds adapted to cold conditions show greater changes in range size related to past climatic oscillations than temperate birds

Investigation of ecological responses of species to past climate oscillations provides crucial information to understand the effects of global warming. In this work, we investigated how past climate changes affected the distribution of six bird species with different climatic requirements and migratory behaviours in the Western Palearctic and in Africa. Species Distribution Models and Marine Isotopic Stage (MIS) 2 fossil occurrences of selected species were employed to evaluate the relation between changes in range size and species climatic tolerances. The Last Glacial Maximum (LGM) range predictions, generally well supported by the MIS 2 fossil occurrences, suggest that cold-dwelling species considerably expanded their distribution in the LGM, experiencing more pronounced net changes in range size compared to temperate species. Overall, the thermal niche proves to be a key ecological trait for explaining the impact of climate change in species distributions. Thermal niche is linked to range size variations due to climatic oscillations, with cold-adapted species currently suffering a more striking range reduction compared to temperate species. This work also supports the persistence of Afro-Palearctic migrations during the LGM due to the presence of climatically suitable wintering areas in Africa even during glacial maxima.

Phenological sensitivity and seasonal variability explain climate-driven trends in Mediterranean butterflies.

Although climate-driven phenological shifts have been documented for many taxa across the globe, we still lack knowledge of the consequences they have on populations. Here, we used a comprehensive database comprising 553 populations of 51 species of north-western Mediterranean butterflies to investigate the relationship between phenology and population trends in a 26-year period. Phenological trends and sensitivity to climate, along with various species traits, were used to predict abundance trends. Key ecological traits accounted for a general decline of more than half of the species, most of which, surprisingly, did not change their phenology under a climate warming scenario. However, this was related to the regional cooling in a short temporal window that includes late winter and early spring, during which most species concentrate their development. Finally, we demonstrate that phenological sensitivity—but not phenological trends—predicted population trends, and argue that species that best adjust their phenology to inter-annual climate variability are more likely to maintain a synchronization with trophic resources, thereby mitigating possible negative effects of climate change. Our results reflect the importance of assessing not only species' trends over time but also species’ abilities to respond to a changing climate based on their sensitivity to temperature.

Determinants of Insecticide Resistance Evolution: Comparative Analysis Among Heliothines.

It is increasingly clear that pest species vary widely in their propensities to develop insecticide resistance. This review uses a comparative approach to analyze the key pest management practices and ecological and biochemical or genetic characteristics of the target that contribute to this variation. We focus on six heliothine species, three of which, Helicoverpa armigera, Heliothis virescens, and Helicoverpa zea, have developed resistances to many pesticide classes. The three others, Helicoverpa punctigera, Helicoverpa assulta, and Helicoverpa gelotopoeon, also significant pests, have developed resistance to very few pesticide classes. We find that host range and movement between alternate hosts are key ecological traits that influence effective selection intensities for resistance. Operational issues are also critical; area-wide, cross-pesticide management practices that account for these ecological factors are key to reducing selection intensity. Without such management, treatment using broad-spectrum chemicals serves to multiply the effects of host plant preference, preadaptive detoxification ability, and high genetic diversity to create a pesticide treadmill for the three high-propensity species.Without rigorous ongoing management, such a treadmill could still develop for newer, more selective chemistries and insecticidal transgenic crops.

Geographic contact drives increased reproductive isolation in two cryptic Empidonax flycatchers.

Geographic contact between sister lineages often occurs near the final stages of speciation, but its role in speciation's completion remains debated. Reproductive isolation may be essentially complete prior to secondary contact. Alternatively, costly interactions between partially reproductively isolated species - such as maladaptive hybridization or competition for resources - may select for divergence, increasing reproductive isolation and driving speciation toward completion. Here, we use coalescent demographic modelling and whole-genome data sets to show that a period of contact and elevated hybridization between sympatric eastern North American populations of two cryptic bird species preceded a major increase in reproductive isolation between these populations within the last 10,000years. In contrast, substantial introgression continues to the present in a western contact zone where geographic overlap is much narrower and probably of more recent origin. In the sympatric eastern region where reproductive isolation has increased, it is not accompanied by character displacement in key morphometric traits, plumage coloration, or ecological traits. While the precise trait and underlying mechanism driving increased reproductive isolation remains unknown, we discuss several possibilities and outline avenues for future research. Overall, our results highlight how demographic models can reveal the geographic context in which reproductive isolation was completed, and demonstrate how contact can accelerate the final stages of speciation.