The effect of mainland dynamics on data and parameter estimates in island biogeography

Understanding macroevolution on islands requires knowledge of the closest relatives of island species on the mainland. The evolutionary relationships between island and mainland species can be reconstructed using phylogenies, to which models can be fitted to understand the dynamical processes of colonisation and diversification. But how much information on the mainland is needed to gain insight into macroevolution on islands? Here we first test whether species turnover on the mainland and incomplete mainland sampling leave recognisable signatures in community phylogenetic data. We find predictable phylogenetic patterns: colonisation times become older and the perceived proportion of endemic species increases as mainland turnover and incomplete knowledge increase. We then analyse the influence of these factors on the inference performance of the island biogeography model DAISIE, a whole-island community phylogenetic model that assumes that mainland species do not diversify, and that the mainland is fully sampled in the phylogeny. We find that colonisation and diversification rate are estimated with little bias in the presence of mainland extinction and incomplete sampling. By contrast, the rate of anagenesis is overestimated under high levels of mainland extinction and incomplete sampling, because these increase the perceived level of island endemism. We conclude that community-wide phylogenetic and endemism datasets of island species carry a signature of mainland extinction and sampling. The robustness of parameter estimates suggests that island diversification and colonisation can be studied even with limited knowledge of mainland dynamics.

Relative palatability and efficacy of brodifacoum-25D conservation rodenticide pellets for mouse eradication on Midway Atoll

Invasive mice (Mus spp.) can negatively impact island species and ecosystems. Because fewer island rodent eradications have been attempted for mice compared to rats (Rattus spp.), less is known about efficacy and palatability of rodenticide baits for mouse eradications. We performed a series of bait acceptance and efficacy cage trials using a standard formulation of brodifacoum-based rodenticide on wild-caught mice from Sand Island, Midway Atoll, to help inform a proposed eradication there. Mice were offered ad libitum brodifacoum pellets along with various alternative food sources, and a “no choice” treatment group received only bait pellets. Mortality in the no choice trial was 100%; however, when offered alternative foods, mice preferred the alternative diets to the bait, leading to low mortality (40%). Because there was concern that the bittering agent Bitrex® in the formulation may have reduced palatability, we conducted a subsequent trial comparing brodifacoum bait with and without Bitrex. Mortality in the with-Bitrex treatment group was slightly higher, indicating that the bittering agent was not likely responsible for low efficacy. Laboratory trials cannot account for the numerous environmental and behavioral factors that influence bait acceptance nor replicate the true availability of alternative food sources in the environment, so low efficacy results from these trials should be interpreted cautiously and not necessarily as a measure of the likelihood of success or failure of a proposed eradication.

Reduction in population size and not a shift in parasite community affect evolution of immune genes in island birds.

Shared ecological conditions encountered by species that colonize islands often lead to the evolution of convergent phenotypes, commonly referred to as "island syndrome". Reduced immune functions have been previously proposed to be part of the island syndrome, as a consequence of the reduced diversity of pathogens on island ecosystems. According to this hypothesis, immune genes are expected to exhibit genomic signatures of relaxed selection pressure in island species. In this study, we used comparative genomic methods to study immune genes in island species (N = 20) and their mainland relatives (N = 14). We gathered public data as well as generated new data on innate (Toll-Like Receptors, Beta Defensins) and acquired immune genes (Major Histocompatibility Complex classes I and II), but also on hundreds of genes annotated as involved in various immune functions. As a control, we used a set of 97 genes not involved in immune functions, to account for the lower effective population sizes in island species. We used synonymous and non-synonymous variations to estimate the selection pressure acting on immune genes. For the genes evolving under balancing selection, we used simulation to estimate the impact of population size variation. We found a significant effect of drift on immune genes of island species leading to a reduction in genetic diversity and efficacy of selection. However, the intensity of relaxed selection was not significantly different from control genes, except for MHC class II genes. These genes exhibit a significantly higher level of non-synonymous loss of polymorphism than expected assuming only drift and an evolution under frequency dependent selection, possibly due to a reduction of extracellular parasite communities on islands. Overall, our results showed that demographic effects lead to a decrease in the immune functions of island species, but the relaxed selection caused by a reduced parasite pressure may only occur in some immune genes categories.

Evolution of New Zealand's Marine Caddisflies: A Phylogenetic and Phylogeographic Assessment of the Chathamiidae (Insecta: Trichoptera)

<p><b>The Chathamiidae are an interesting family of caddisflies, unusual as all of the five known species are believed to breed entirely within the marine intertidal, comprising one of very few known marine insect groups. Additionally the family approaches almost complete endemicity status in New Zealand, and may represent an ancient lineage representative of ancient vicariance from Gondwana. However one species, the common and widespread Philanisus plebeius is also known to have a disjunct population in New South Wales Australia, hypothesised to represent a recent anthropogenic dispersal. This thesis, using DNA information, examined the Chathamiidae at varying phylogenetic levels.</b></p> <p>Firstly the species Philanisus plebeius was incorporated into a thorough intraspecific phylogeography, including samples from both New Zealand and Australia. The population as a whole was genetically diverse, with the population divisible into two major haplogroups, each restricted to discrete geographic areas with no overlap being observed. One of these groups was restricted to just two localities in the central eastern North Island, whereas the remainder included most remaining samples from both Islands of New Zealand, and also Australia. All Australian samples were found to comprise a single haplotype, differing by a single base pair from the most common haplotype in New Zealand. It was decided that the Australian population therefore represents a recent dispersal event from New Zealand, although unless the Australian haplotype remains undiscovered in New Zealand the level of divergence found is not congruent with a human introduction. One sequence intermediate between the two major haplogroups was identified from a single haplotype from Tauranga. It seemed that much of the population of Philanisus plebeius has been affected by recent demographic expansion, likely due to the effects of the last glacial maximum (LGM).</p> <p>The five species of the Chathamiidae were then analysed in a phylogeny. It was found that the genus Chathamia was polyphyletic, with the species C. integripennis nested within the genus Philanisus. The remaining species, C. brevipennis from the Chatham Islands, was basal to all the remaining members of the family. A strict molecular clock found a recent Pleistocene age (roughly 0.5 Ma) for divergence of the Kermadec Island species Philanisus fasciatus, and a Pliocene-Pleistocene age (roughly 3 Ma) for the Chatham Island species Chathamia brevipennis. For a comparison with the species C. brevipennis, the other Chatham Island caddisfly taxa Oecetis chathamensis, and Hydrobiosis lindsayi were compared with New Zealand relatives; indicated to have late and early Pleistocene ages respectively. A short sequence of the gene COI was amplified for the species Philanisus mataua, however this was found to contain two sequences reflecting either heteroplasmy or sample contamination, inhibiting confident phylogenetic placement. Additionally a larval sample from Sydney was demonstrated to represent C. integripennis, recorded outside of Northern New Zealand for the first time. Finally the Chathamiidae was included in a higher level phylogeny with related families, and was show to comprise a monophyletic group, sister to the Australasian family of the Conoesucidae. A relaxed molecular clock estimated a Cretaceous (roughly 90 Ma) age for the Chathamiidae, congruent with a vicariant age in New Zealand.</p>

Evolution of New Zealand's Marine Caddisflies: A Phylogenetic and Phylogeographic Assessment of the Chathamiidae (Insecta: Trichoptera)

<p><b>The Chathamiidae are an interesting family of caddisflies, unusual as all of the five known species are believed to breed entirely within the marine intertidal, comprising one of very few known marine insect groups. Additionally the family approaches almost complete endemicity status in New Zealand, and may represent an ancient lineage representative of ancient vicariance from Gondwana. However one species, the common and widespread Philanisus plebeius is also known to have a disjunct population in New South Wales Australia, hypothesised to represent a recent anthropogenic dispersal. This thesis, using DNA information, examined the Chathamiidae at varying phylogenetic levels.</b></p> <p>Firstly the species Philanisus plebeius was incorporated into a thorough intraspecific phylogeography, including samples from both New Zealand and Australia. The population as a whole was genetically diverse, with the population divisible into two major haplogroups, each restricted to discrete geographic areas with no overlap being observed. One of these groups was restricted to just two localities in the central eastern North Island, whereas the remainder included most remaining samples from both Islands of New Zealand, and also Australia. All Australian samples were found to comprise a single haplotype, differing by a single base pair from the most common haplotype in New Zealand. It was decided that the Australian population therefore represents a recent dispersal event from New Zealand, although unless the Australian haplotype remains undiscovered in New Zealand the level of divergence found is not congruent with a human introduction. One sequence intermediate between the two major haplogroups was identified from a single haplotype from Tauranga. It seemed that much of the population of Philanisus plebeius has been affected by recent demographic expansion, likely due to the effects of the last glacial maximum (LGM).</p> <p>The five species of the Chathamiidae were then analysed in a phylogeny. It was found that the genus Chathamia was polyphyletic, with the species C. integripennis nested within the genus Philanisus. The remaining species, C. brevipennis from the Chatham Islands, was basal to all the remaining members of the family. A strict molecular clock found a recent Pleistocene age (roughly 0.5 Ma) for divergence of the Kermadec Island species Philanisus fasciatus, and a Pliocene-Pleistocene age (roughly 3 Ma) for the Chatham Island species Chathamia brevipennis. For a comparison with the species C. brevipennis, the other Chatham Island caddisfly taxa Oecetis chathamensis, and Hydrobiosis lindsayi were compared with New Zealand relatives; indicated to have late and early Pleistocene ages respectively. A short sequence of the gene COI was amplified for the species Philanisus mataua, however this was found to contain two sequences reflecting either heteroplasmy or sample contamination, inhibiting confident phylogenetic placement. Additionally a larval sample from Sydney was demonstrated to represent C. integripennis, recorded outside of Northern New Zealand for the first time. Finally the Chathamiidae was included in a higher level phylogeny with related families, and was show to comprise a monophyletic group, sister to the Australasian family of the Conoesucidae. A relaxed molecular clock estimated a Cretaceous (roughly 90 Ma) age for the Chathamiidae, congruent with a vicariant age in New Zealand.</p>

Low diversity, little genetic structure but no inbreeding in a high density island endemic pit-viper Gloydius shedaoensis

Islands species and their ecosystems play an important role in global biodiversity preservation, and many vulnerable island species are conservation priorities. Although insular habitat likely facilitates the species diversification process, it may also aggravate the fragility of these species with high risk of inbreeding. The Shedao pit-viper Gloydius shedaoensis is an island endemic species with an extremely high population density, which has been categorized as vulnerable in the IUCN Red List. We collected 13,148 SNP from across its genome and examined its genetic diversity and demographic history. The Shedao pit-viper has a low genetic diversity but shows no sign of inbreeding. Furthermore, population genetic structure analysis, including the NJ tree, PCoA, clustering, and spatial autocorrelation, revealed a general lack of spatial structure. Only the IBD residues suggested a weak patchiness. Overall, the population is nearly panmictic and gene flow is evenly distributed across the island. The large number of individuals, small size of the island, and the lack of population structure likely all contribute to the lack of inbreeding in this species. We also detected signs of male-biased dispersal, which likely is another inbreeding avoidance strategy. Historical demographic analysis suggested that the historical population size and distribution of the species are much larger than their current ones. The multiple transgressive-regressive events since the Late Pleistocene are likely the main cause of the population size changes. Taken together, our results provide a basic scientific foundation for the conservation of this interesting and important species.

Evaluating the correlation between area, environmental heterogeneity, and species richness using terrestrial isopods (Oniscidea) from the Pontine Islands (West Mediterranean)

Area and environmental heterogeneity influence species richness in islands. Whether area or environmental heterogeneity is more relevant in determining species richness is a central issue in island biogeography. Several models have been proposed, addressing the issue, and they can be reconducted to three main hypotheses developed to explain the species-area relationship: (1) the area-per se hypothesis (known also as the extinction-colonisation equilibrium), (2) the random placement (passive sampling), and the (3) environmental heterogeneity (habitat diversity). In this paper, considering also the possible influence of geographic distance on island species richness, we explore the correlation between area, environmental heterogeneity, and species richness by using faunistic data of Oniscidea inhabiting the Pontine Islands, a group of five small volcanic islands and several islets in the Tyrrhenian Sea, located about 60 km from the Italian mainland. We found that the colonisation of large Pontine Islands may occur via processes independent of geographic distance which could instead be an important factor at a much smaller scale. Such processes may be driven by a combination of anthropogenic influences and natural events. Even in very small-size island systems, environmental heterogeneity mostly contributes to species richness. Environmental heterogeneity could influence the taxocenosis structure and, ultimately, the number of species of Oniscidea via direct and indirect effects, these last mediated by area which may or may not have a direct effect on species richness.

The conservation and ecology of the British Virgin Islands endemic tree, Vachellia anegadensis

Numerous island species have gone extinct and many extant, but threatened, island endemics require ongoing monitoring of their conservation status. The small tree Vachellia anegadensis was formerly thought to occur only on the limestone island of Anegada in the British Virgin Islands and was categorized as Critically Endangered. However, in 2008 it was discovered on the volcanic island of Fallen Jerusalem, c. 35 km from Anegada, and in 2018 it was recategorized as Endangered. To inform conservation interventions, we examined the species’ distribution, genetic population structure, dependency on pollinators and preferred habitat, and documented any threats. We found V. anegadensis to be locally widespread on Anegada but uncommon on Fallen Jerusalem and established that geographical location does not predict genetic differentiation amongst populations. Vachellia anegadensis produces the highest number of seed pods when visited by animal pollinators, in particular Lepidoptera. Introduced animals and disturbance by humans appear to be the main threats to V. anegadensis, and in situ conservation is critical for the species’ long-term survival.

The Allometry of Morphology in Flora and Fauna of New Zealand and Offshore Islands

<p>Flight is the primary form of locomotion for many avian species and is enabled by allometric scaling of morphological features such as wingspan, flight muscle size, and bone tensile strength. Contrary to this, the evolution of flightlessness in birds displays a selection towards an increase in body size with a reduction in flight associated features. The aim of this chapter is to explore the Loss of Dispersibility hypothesis as a cause for flightlessness in island birds, with consideration of the Island Rule and the Size-Constraint hypothesis. With island species paired with closest mainland relatives, comparative analyses were conducted comparing the change in wing loading ratios, wing lengths, and mass. With paired t-tests and Major Axis linear regression modelling, the hypotheses of isometric or allometric scaling in each of the features were tested. An increase in wing-loading ratio was apparent for many island species, as well as an increase in both mass and wing length. However, the rate of increase between mass and wing length is disproportionate, with mass increasing at a greater rate than wing length. These trends reject the Loss of Dispersibility hypothesis in support of the Size-Constraint hypothesis while providing little evidence for the Island Rule.</p>