Are subspecies of Anolis lizards that differ in dewlap color and pattern also genetically distinct? A mitochondrial analysis

Subspecies of Anolis lizards are often defined on the basis of geographic variation in the color and pattern of the dewlap, an extensible throat fan considered central to species recognition and sexual selection. Among the most impressive examples of this phenomenon are two species of trunk anoles found across Hispaniola and the Bahamas: Anolis distichus is divided into 16 subspecies with dewlap colors ranging from deep wine red to pale yellow while Anolis brevirostris is divided into three subspecies with dewlaps ranging from pale yellow to orange. Limited sampling of allozyme data indicates some genetic divergence among subspecies and suggests that they may deserve recognition at the species-level. Our goal here is to use more comprehensive geographic sampling of mtDNA haplotypes to test whether the five subspecies of A. distichus and three subspecies of A. brevirostris that occur in the Dominican Republic correspond with genetically distinct populations that may warrant recognition under the general lineage concept. We obtain an aligned dataset of 1462bp comprised of the genes encoding ND2 and adjacent tRNAs from 76 individuals of A. distichus from 28 localities and 12 individuals of A. brevirostris from five localities. We find that haplotypes sampled from each Dominican subspecies of A. distichus form well-supported and deeply divergent clades (>10% uncorrected sequence divergence). Strong concordance between mtDNA haplotype structure and previously diagnosed phenotypic variation in traits central to interspecific communication (i.e., the dewlap) leads us to hypothesize that each of the presently recognized Dominican subspecies of A. distichus and A. brevirostris deserves elevation to full species status under the general lineage concept.     

Stick or grip? Co-evolution of adhesive toepads and claws in Anolis lizards

Exploring the relationship between phenotype and performance in an ecological and evolutionary context is crucial to understanding the adaptive nature of phenotypic traits. Despite their ubiquity in vertebrates, few studies have examined the functional and ecological significance of claw morphologies. Here we examine the adhesive toepad and claw system of Anolis lizards. Claw characters are significantly different between lizards classified as arboreal (perch height ≥ 1 m) and non-arboreal (perch height < 1 m). Arboreal species possess significantly higher and longer claws, and show trends toward decreased claw curvature and wider claw tip angles. Toepad size and claw length and height are tightly correlated with each other and with perch height, suggesting that the adhesive toepad and gripping claw have co-evolved to accommodate different habitats. The functional morphology and evolution of claws are ripe areas for future investigation.     

What determines the relationship between plant diversity and habitat productivity?

The relationship between biodiversity and habitat productivity has been a fundamental topic in ecology. Although the relationship between these parameters may exhibit different shapes, the unimodal shape has been frequently encountered. The decrease in diversity at high productivity has usually been attributed to competitive exclusion. We suggest that evolutionary history and dispersal limitation may be even more important in shaping the diversity–productivity relationship. On a global scale, unimodal diversity–productivity relationships dominate in temperate regions, whereas positive relationships are more common in the tropics. This difference can be accounted for by contrasting evolutionary history. Temperate regions have smaller species pools for productive habitats since these habitats have been scarce historically for speciation, while the opposite is true for the tropics. In addition, dispersal within a region may limit diversity either due to the lack of dispersal syndromes at low productivity or the low number of diaspores at high productivity. Thereafter, biotic interactions (competition and facilitation) can shape the relationship. All these processes can act independently or concurrently. We recommend that the common approach to examining empirical diversity–environmental relationships should start with the role of large‐scale processes such as evolutionary history and dispersal limitation, followed by influences associated with ecological interactions.     

What determines host range in parasitoids? An analysis of a tachinid parasitoid community

Despite the vast diversity of parasitic insects and their importance in natural and agricultural communities, our knowledge of what determines their patterns of association with hosts remains sparse. Unlike most parasites that tend to be specialized, parasitoid flies in the family Tachinidae exhibit a broad spectrum of host-specificity, with many species attacking a wide range of hosts. This variability in host-specificity makes them a useful model for examining the ecological and historical factors that determine host associations. We analyzed data collected from a 5-year rearing program of Lepidoptera in southern Arizona to investigate the factors that influence tachinid-host associations. After controlling for a strong effect of sample size, a significant portion of the remaining variance in host range was explained by differences among phylogenetic groups of tachinids and/or their correlated reproductive strategies. Relatively specialized tachinids tended to be associated with monophagous or narrowly oligophagous hosts and attacked them at relatively high frequencies, a pattern we suggest is related to host location efficiency. Cluster analysis indicated that host abundance, gregariousness, food-plant type, and morphology are all important determinants of tachinid host use. Little concordance was found between how tachinid species cluster according to characteristics of their hosts and their estimated phylogenetic relationships. Together, the results of this study suggest that ecological factors are important determinants of host use in these parasitoids and although phylogenetic history may influence the range of hosts used, its power to explain the ecological or taxonomic character of hosts used appears limited.     

What factors shape genetic diversity in cetaceans?

Understanding what factors drive patterns of genetic diversity is a central aspect of many biological questions, ranging from the inference of historical demography to assessing the evolutionary potential of a species. However, as a larger number of datasets have become available, it is becoming clear that the relationship between the characteristics of a species and its genetic diversity is more complex than previously assumed. This may be particularly true for cetaceans, due to their relatively long lifespans, long generation times, complex social structures, and extensive ranges. In this study, we used microsatellite and mitochondrial DNA data from a systematic literature review to produce estimates of diversity for both markers across 42 cetacean species. Factors relating to demography, distribution, classification, biology, and behavior were then tested using phylogenetic methods and linear models to assess their relative influence on the genetic diversity of both marker types. The results show that while relative nuclear diversity is correlated with population size, mitochondrial diversity is not. This is particularly relevant given the widespread use of mitochondrial DNA to infer historical demography. Instead, mitochondrial diversity was mostly influenced by the range and social structure of the species. In addition to population size, habitat type (neritic vs. oceanic) had a significant correlation with relative nuclear diversity. Combined, these results show that many often‐unconsidered factors are likely influencing patterns of genetic diversity in cetaceans, with implications regarding how to interpret, and what can be inferred from, existing patterns of diversity.     

Genetic drift or natural selection? Hybridization and asymmetric mitochondrial introgression in two Caribbean lizards (Anolis pulchellus and Anolis krugi)

Hybridization and gene introgression can occur frequently between closely related taxa, but appear to be rare phenomena among members of the species‐rich West Indian radiation of Anolis lizards. We investigated the pattern and possible mechanism of introgression between two sister species from Puerto Rico, Anolis pulchellus and Anolis krugi, using mitochondrial (ND2) and nuclear (DNAH3, NKTR) DNA sequences. Our findings demonstrated extensive introgression of A. krugi mtDNA (k‐mtDNA) into the genome of A. pulchellus in western Puerto Rico, to the extent that k‐mtDNA has mostly or completely replaced the native mtDNA of A. pulchellus on this part of the island. We proposed two not mutually exclusive scenarios to account for the interspecific matings between A. pulchellus and A. krugi. We inferred that hybridization events occurred independently in several populations, and determined that k‐mtDNA haplotypes harboured in individuals of A. pulchellus can be assigned to four of the five major mtDNA clades of A. krugi. Further, the spatial distribution of k‐mtDNA clades in the two species is largely congruent. Based on this evidence, we concluded that natural selection was the probable driving mechanism for the extensive k‐mtDNA introgression into A. pulchellus. Our two nuclear data sets yielded different results. DNAH3 showed reciprocal monophyly of A. pulchellus and A. krugi, indicating no effect of hybridization on this marker. In contrast, the two species shared nine NKTR alleles, probably due to incomplete lineage sorting. Our study system will provide an excellent opportunity to experimentally assess the behavioural and ecological mechanisms that can lead to hybridization in closely related taxa.     

Evolutionary trade‐offs in locomotor capacities in lacertid lizards: are splendid sprinters clumsy climbers?

We tested the hypothesis that an evolutionary trade‐off exists between the capacity to run on level terrain and the ability to climb inclined structures in lacertid lizards. Biomechanical and physiological models of lizard locomotor performance suggest that the morphological design requirements of a ground‐dwelling vs. scansorial life style are difficult to reconcile. This conflict is thought to preclude simultaneous evolution of maximal locomotor performance on level and inclined terrain. This notion has been corroborated by comparative studies on lizard species from other groups (Anolis, Chamaeleo, Sceloporus), but is not supported by our data on 13 species from the family Lacertidae. We found no indication of a negative association between maximal sprint speed of lizards over a level racetrack (indicative of ground‐dwelling locomotor performance), on an inclined stony surface (indicative of climbing performance over rock faces) and inclined mesh surface (indicative of clambering performance among vegetation). Moreover, morphological characteristics associated with fast sprinting capacities (e.g. long hind limbs) apparently enhance, rather than hinder climbing and clambering performance. We conclude that in our sample of lacertid lizards, the evolution of fast sprinting capacity on level terrain has not inflicted major restrictions on climbing and clambering performance.     

What determines species composition and diversity of hypogeous fungi in the diet of small mammals? A comparison across mammal species,habitat types and seasons in Central European mountains

Interactions between diverse groups of organisms influence the functioning and diversity of ecosystems. Salient examples of such relationships are those among hypogeous fungi, trees and mycophagous mammals. To investigate the role of small mammals in transporting fungal spores within and outside forests as well as the influence of seasons, habitats and species on small mammal mycophagy, we set up a study in the Pieniny Mts, Western Carpathians (Southern Poland). The droppings of small mammals were collected during live trapping in July and September 2016 and 2017, to analyze richness, composition and frequency of fungal spores present in faeces. The yellow-necked mouse Apodemus flavicollis, the bank vole Myodes glareolus and the common vole Microtus arvalis were the most frequently trapped. Spores of 27 fungal taxa from 16 genera were retrieved from nearly 70% of faecal samples of rodents and shrews, with up to 9 spore taxa recorded per sample. Spore diversity in samples was higher in September than in July, although seasonal variation was year and animal dependent. The highest mean number of fungal taxa per sample was recorded for the bank vole and the yellow-necked mouse, with the former species showing a higher degree of mycophagy. The two rodents differed in the average frequencies of consumed fungi in samples, which could result from some degree of specialization in the choice of particular fungal species, as shown by the laboratory-based experiment. Within particular animal species, differences in the fungal diet were found between seasons. The spores of hypogeous fungi were transported from forests to meadows mostly by the yellow-necked mouse and, to a lesser extent, by the common vole. However, both, the diversity and the number of transported spores diminished with distance from the forest edge.     

Do weaver ants affect arthropod diversity and the natural‐enemy‐to‐pest ratio in horticultural systems?

High biodiversity is an important component of sustainable agricultural systems, and previous studies have found that increases in the diversity of the natural enemies of pests are associated with decreases in pest populations. Weaver ants are well known for their highly territorial and aggressive behaviour and for their control efficiency of many insect pests in tropical crop trees. Because of this, the ants have been used as a key component in integrated pest management (IPM) programmes for tropical crop trees. In implementing the IPM programmes, we received a number of enquiries related to whether weaver ants have negative effects on arthropod diversity and other natural enemies in orchard systems due to their aggressive behaviour. To answer these questions, we regularly sampled canopy arthropods in cashew and mango orchards in the Northern Territory of Australia in 1996, 2002 and 2003. We sampled, using a vacuum sampler, orchards with and without weaver ants. Cashew and mango plots with abundant weaver ants had similar or higher canopy arthropod and natural enemy diversity and similar ratios of natural enemies to insect pests, compared with plot where the weaver ant was absent. The study also showed that the application of insecticides reduced arthropod diversity and the ratio of natural enemies to insect pests in a mango orchard. However, insecticide spray did not affect natural enemy diversity and abundance, which may be related to a high immigration rate of natural enemies in small plots surrounded by areas that were not sprayed.     

The small‐island effect: fact or artefact?

Positive relationships between species richness and sampling area are perhaps the most pervasive patterns in nature. However, the shape of species–area relationships is often highly variable, for reasons that are poorly understood. One such source of variability is the "small-island effect", which refers to a decrease in the capacity of sampling area to predict species richness on small islands. Small-island effects have been attributed to a variety of processes, including spatial subsidies, habitat characteristics and ocean-born disturbances. Here, we show that small-island effects can be generated by logarithmic data transformations, which are commonly applied to both axes of species–area relationships. To overcome this problem, we derive several null models to test for non-random variability in the capacity of island area to predict species richness and apply them to data sets on island plant communities in Canada and New Zealand. Both archipelagos showed evidence for small-island effects using traditional breakpoint regression techniques on log-log axes. However, null model analyses revealed different results. The capacity of sampling area to predict species richness in the Canadian archipelago was actually lowest at intermediate island size classes. In the New Zealand archipelago, island area was similarly capable of predicting species richness across the full range of island sizes, indicating the small-island effect detected by breakpoint regression is an artifact of logarithm data transformation. Overall results show that commonly used regression techniques can generate spurious small-island effects and that alternative analytic procedures are needed to detect non-random patterns in species richness on small islands.     

What determines the growth of individual castes in social trematodes?

Phenotypic diversification among colony members often leads to formation of physical castes which are morphologically specialised for particular tasks within the colony. The relative abundance of these castes and their body sizes represent two key aspects of the demography of a colony that may reflect the colony’s needs and conditions, and ultimately influence its survival and reproductive success. In a recently discovered social trematode, Philophthalmus sp., which exhibits a reproductive division of labour, the role of competition and colony composition in shaping reproductive success and behaviour of colony members has been documented. As body size variation within physical castes often influences colony efficiency, we investigated how the growth of reproductive and non-reproductive morphs of Philophthalmus sp. responds to competitive pressure, and to other attributes of colony demography such as colony size and composition. Our survey of a natural population and in vitro experiments demonstrate that the growth of reproductive colony members reflects the interaction between colony composition and the presence of a competitor, while the non-reproductive members simply grow larger in the presence of the intra-host competitor, Maritrema novaezealandensis. Furthermore, the close association between the volume and reproductive capacity of the reproductive members corroborates an adaptive value of colony member size in determining the fitness of the trematode colony as a whole. The present study is the first to demonstrate a fitness consequence, and identify the determinants, of the growth of colony members in social trematodes.     

Does adaptive radiation of a host lineage promote ecological diversity of its bacterial communities? A test using gut microbiota of Anolis lizards

Adaptive radiations provide unique opportunities to test whether and how recent ecological and evolutionary diversification of host species structures the composition of entire bacterial communities. We used 16S rRNA gene sequencing of faecal samples to test for differences in the gut microbiota of six species of Puerto Rican Anolis lizards characterized by the evolution of distinct ‘ecomorphs’ related to differences in habitat use. We found substantial variation in the composition of the microbiota within each species and ecomorph (trunk‐crown, trunk‐ground, grass‐bush), but no differences in bacterial alpha diversity among species or ecomorphs. Beta diversity analyses revealed subtle but significant differences in bacterial composition related to host phylogeny and species, but these differences were not consistently associated with Anolis ecomorph. Comparison of a trunk‐ground species from this clade (A. cristatellus) with a distantly related member of the same ecomorph class (A. sagrei) where the two species have been introduced and are now sympatric in Florida revealed pronounced differences in the alpha diversity and beta diversity of their microbiota despite their ecological similarity. Comparisons of these populations with allopatric conspecifics also revealed geographic differences in bacterial alpha diversity and beta diversity within each species. Finally, we observed high intraindividual variation over time and strong effects of a simplified laboratory diet on the microbiota of A. sagrei. Collectively, our results indicate that bacterial communities are only weakly shaped by the diversification of their lizard hosts due to the strikingly high levels of bacterial diversity and variation observed within Anolis species.     

Does ecological specialization transcend scale? Habitat partitioning among individuals and species of Anolis lizards

Ecological specialization is common across all levels of biological organization, raising the question of whether the evolution of specialization at one scale in a taxon is linked to specialization at other scales. Anolis lizards have diversified repeatedly along axes of habitat use, but it remains unknown if this diversification into habitat use specialists is underlain by individual specialization. From repeated observations of individuals in a population of Anolis sagrei in Florida, we show that the extent of habitat use specialization among individuals is comparable to the extent of specialization in the same traits among ten sympatric Anolis habitat specialist species in Cuba. However, the adaptive correlations between habitat use and morphology commonly seen across species of Anolis were not observed across individuals in the sampled population. Our results therefore suggest that while patterns of ecological specialization can transcend scale, these parallels are the consequence of distinct ecological processes acting at microevolutionary and macroevolutionary scales.     

Is genomic diversity a useful proxy for census population size? Evidence from a species‐rich community of desert lizards

Species abundance data are critical for testing ecological theory, but obtaining accurate empirical estimates for many taxa is challenging. Proxies for species abundance can help researchers circumvent time and cost constraints that are prohibitive for long‐term sampling. Under simple demographic models, genetic diversity is expected to correlate with census size, such that genome‐wide heterozygosity may provide a surrogate measure of species abundance. We tested whether nucleotide diversity is correlated with long‐term estimates of abundance, occupancy and degree of ecological specialization in a diverse lizard community from arid Australia. Using targeted sequence capture, we obtained estimates of genomic diversity from 30 species of lizards, recovering an average of 5,066 loci covering 3.6 Mb of DNA sequence per individual. We compared measures of individual heterozygosity to a metric of habitat specialization to investigate whether ecological preference exerts a measurable effect on genetic diversity. We find that heterozygosity is significantly correlated with species abundance and occupancy, but not habitat specialization. Demonstrating the power of genomic sampling, the correlation between heterozygosity and abundance/occupancy emerged from considering just one or two individuals per species. However, genetic diversity does no better at predicting abundance than a single day of traditional sampling in this community. We conclude that genetic diversity is a useful proxy for regional‐scale species abundance and occupancy, but a large amount of unexplained variation in heterozygosity suggests additional constraints or a failure of ecological sampling to adequately capture variation in true population size.