Genetic differentiation of island populations: geographical barrier or a host switch?

In the Sonoran desert, there exists a diverse community of cactophilic drosophilids that exploit toxic, rotting cactus tissue as a food resource. The chemistry of the necrotic cactus tissue varies among species, and several drosphilid species have evolved specialized detoxification mechanisms and a preference for certain cactus types. In the present study, we compared the genetic structure of two columnar cactus species, Drosophila mettleri and Drosophila mojavensis, and two prickly pear species, Drosophila mainlandi and Drosophila hamatofila, which have all recently colonized Catalina Island off the coast of southern California. Because there are no columnar cactus species on Catalina Island, the two columnar specialists underwent a host switch to prickly pear cactus, the only cactus present on the island. Previous genetic studies of D. mettleri and D. mojavensis showed significant genetic differentiation between mainland and island populations, which could result from restricted gene flow as a result of the San Pedro Channel, or because of a host switch to prickly pear. To distinguish between these possibilities, we analyzed the genetic structure of the prickly pear species aiming to isolate the effects of geography versus host switching. The results obtained show little to no genetic differentiation for the prickly pear species, supporting the hypothesis that the genetic differentiation of the two columnar species is a result of a host switch from columnar cacti to prickly pear. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Clustered or scattered? The impact of habitat quality clustering on establishment and early spread

The match between the environmental conditions of an introduction area and the preferences of an introduced species is the first prerequisite for establishment. Yet, introduction areas are usually landscapes, i.e. heterogeneous sets of habitats that are more or less favourable to the introduced species. Because individuals are able to disperse after their introduction, the quality of the habitat surrounding the introduction site is as critical to the persistence of introduced populations as the quality of the introduction site itself. Moreover, demographic mechanisms such as Allee effects or dispersal mortality can hamper dispersal and affect spread across the landscape, in interaction with the spatial distribution of favourable habitat patches. In this study, we investigate the impact of the spatial distribution of heterogeneous quality habitats on establishment and early spread. First, we simulated introductions in one‐dimensional landscapes for different dispersal rates and either dispersal mortality or Allee effects. The landscapes differed by the distribution of favourable and less favourable habitats, which were either clustered into few large aggregates of the same quality or scattered into multiple smaller ones. Second, we tested the predictions of simulations by performing experimental introductions of hymenopteran parasitoids (Trichogramma chilonis) in ‘clustered’ and ‘scattered’ microcosm landscapes. Results highlighted two impacts of the clustering of favourable habitat: by decreasing the risks of dispersal from the introduction site to unfavourable habitat early during the invasion, it increased establishment success. However, by increasing the distance between favourable habitat patches, it also hindered the subsequent spread of introduced species over larger areas.     

Conservation genetics of two island endemic Ribes spp. (Grossulariaceae) of Sardinia: survival or extinction?

Measuring levels of population genetic diversity is an important step for assessing the conservation status of rare or endangered plant species and implementing appropriate conservation strategies. Populations of Ribes multiflorum subsp. sandalioticum and R. sardoum, two endangered endemic species from Sardinia, representing the whole genus on the island, were investigated using ISSR and SSR markers to determine levels and structure of genetic variability in their natural populations. Results indicated medium to low genetic diversity at the population level: Nei's gene diversity for ISSR markers ranged from 0.0840 to 0.1316; the expected heterozygosity (H_E) for SSR ranged from 0.4281 to 0.7012. In addition, only one remnant population of R. sardoum showed a high level of inbreeding, in accordance with its very small size. Regarding the structure of the six R. sandalioticum populations, both principal coordinates analysis (PCoA) and STRUCTURE analysis of ISSR and SSR data highlighted low population structure, although two populations appeared to be clearly distinct from the others. The genetic pattern of the two taxa associated with their different ecological positions indicated resilience of R. sandalioticum populations in fresh and humid habitats and uncertain future resistance for the residual R. sardoum population in xeric calcareous stands. Hence, this study highlights the importance of an integrated conservation approach (genetic plus in situ and ex situ conservation studies/measures) for activating management programmes in these endemic and threatened taxa that can be considered as crop wild relatives of cultivated Ribes species.     

Breeding birds on small islands: island biogeography or optimal foraging?

1. We test MacArthur and Wilson's theory about the biogeography of communities on isolated habitat patches using bird breeding records from 16 small islands off the coasts of Britain and Ireland. 2. A traditional examination of patterns of species richness on these islands suggests that area and habitat diversity are important predictors, but that isolation and latitude have a negligible impact in this system. 3. Unlike traditional studies, we directly examine the fundamental processes of colonization and local extinction (cessation of breeding), rather than higher-order phenomena such as species richness. 4. We find that many of MacArthur and Wilson's predictions hold: colonization probability is lower on more isolated islands, and extinction probability is lower on larger islands and those with a greater diversity of habitats. 5. We also find an unexpected pattern: extinction probability is much lower on more isolated islands. This is the strongest relationship in these data, and isolation is the best single predictor of colonization and extinction. 6. Our results show that examination of species richness alone is misleading. Isolation has a strong effect on both of the dynamic processes that underlie richness, and in this system, the reductions in both colonization and extinction probability seen on more distant islands have opposing influences on species richness, and largely cancel each other out. 7. We suggest that an appropriate model for this system might be optimal foraging theory, which predicts that organisms will stay longer in a resource patch if the distance to a neighbouring patch is large. If nest sites and food are the resources in this system, then optimal foraging theory predicts the pattern we observe. 8. We advance the hypothesis that there is a class of spatial systems, defined by their scale and by the taxon under consideration, at which decision-making processes are a key driver of the spatiotemporal dynamics. The appropriate theory for such systems will be a hybrid of concepts from biogeography/metapopulation theory and behavioural ecology.     

Metacommunity,mainland‐island system or island communities? Assessing the regional dynamics of plant communities in a fragmented landscape

Understanding the regional dynamics of plant communities is crucial for predicting the response of plant diversity to habitat fragmentation. However, for fragmented landscapes the importance of regional processes, such as seed dispersal among isolated habitat patches, has been controversially debated. Due to the stochasticity and rarity of among‐patch dispersal and colonization events, we still lack a quantitative understanding of the consequences of these processes at the landscape‐scale. In this study, we used extensive field data from a fragmented, semi‐arid landscape in Israel to parameterize a multi‐species incidence‐function model. This model simulates species occupancy pattern based on patch areas and habitat configuration and explicitly considers the locations and the shapes of habitat patches for the derivation of patch connectivity. We implemented an approximate Bayesian computation approach for parameter inference and uncertainty assessment. We tested which of the three types of regional dynamics – the metacommunity, the mainland‐island, or the island communities type – best represents the community dynamics in the study area and applied the simulation model to estimate the extinction debt in the investigated landscape. We found that the regional dynamics in the patch‐matrix study landscape is best represented as a system of highly isolated ‘island’ communities with low rates of propagule exchange among habitat patches and consequently low colonization rates in local communities. Accordingly, the extinction rates in the local communities are the main drivers of community dynamics. Our findings indicate that the landscape carries a significant extinction debt and in model projections 33–60% of all species went extinct within 1000 yr. Our study demonstrates that the combination of dynamic simulation models with field data provides a promising approach for understanding regional community dynamics and for projecting community responses to habitat fragmentation. The approach bears the potential for efficient tests of conservation activities aimed at mitigating future losses of biodiversity.     

Does interspecific competition with a stronger competitor explain the rarity of an endangered snake on a Mediterranean island?

Interspecific competition has been demonstrated to be an important shaping force for snake communities worldwide, but relatively few studies have investigated its occurrence and extent with island assemblages of snakes. In Sardinia (Mediterranean Sea), two species of whip snakes (Colubridae) co-occur, one of them being abundant and widespread (Hierophis viridiflavus) and the other being localized and critically endangered (Hemorrhois hippocrepis). A previous hypothesis suggested that the latter species would be confined to suboptimal habitats by the former species, which is a stronger competitor for food. As a consequence, He. hippocrepis would not only be rare but would also be smaller in body size in Sardinia than in other regions of its range where Hi. viridiflavus does not occur. In 1999?C2010, we studied habitat selection, food habits, and body sizes of these two snakes in sympatric populations, applying a suite of statistical tools including null models and Monte Carlo simulations. We observed that dietary habits were different between species (compared to Hi. viridiflavus, He. hippocrepis more frequently preyed upon rodents and less frequently on lizards, and within rodent prey, more frequently upon Rattus and less frequently upon Mus), but not in a way compatible with competitively induced trophic niche partitioning. The two species were similar in terms of prey size and predator-size?Cprey-size relationships. They also differed in habitat selection (maquis was the preferred habitat for both, but Hi. viridiflavus was found significantly more often than He. hippocrepis in grasslands, cultivations, and artificial pinewoods) but again in a non-competitively directed way. In addition, there was no evidence for the hypothesis that He. hippocrepis was confined to suboptimal habitats. Body sizes were similar between species (with males being significantly larger than females), and Sardinian He. hippocrepis were not smaller than conspecifics inhabiting regions without Hi. viridiflavus. Overall, our study showed that the two species differed in some aspects of their ecology, but these differences could not be due to competitive interactions. The conservation implications of these results are also discussed.     

Velvet worm (Phylum Onychophora) on a sand island,in a wetland: Flushed from a Pleistocene refuge by recent rainfall?

Velvet worms (Onychophora) are restricted to moist, humid microclimates, but are poorly known from south‐east Queensland, Australia, where they are typically rainforest fauna. We made the unlikely observation of one of these invertebrates clinging to floating debris in a wetland on North Stradbroke Island. Palaeoecology of this wetland reveals that it once was within rainforest and has remained moist for at least the past 80 000 years, thus potentially harbouring an onychophoran population as a relic of a past broader, rainforest distribution. The presence of this animal, floating in the wetland, can be explained by recent climate, since the wetland filled following heavy rainfall shortly before the observation. This highlights the importance of groundwater‐fed wetlands as evolutionary refugia for moisture‐dependent biota.     

A Dendroctonus bark engraving (Coleoptera: Scolytidae) from a middle Eocene Larix (Coniferales: Pinaceae): early or delayed colonization?

An engraving made by a scolytid bark beetle, assigned to the genus Dendroctonus of the tribe Tomicini, has been identified on a mummified, middle Eocene (45 Ma) specimen of Larix altoborealis wood from the Canadian High Arctic. Larix altoborealis is the earliest known species of Larix, a distinctive lineage of pinaceous conifers that is taxonomically identifiable by the middle Eocene and achieved a broad continental distribution in northern North America and Eurasia during the late Cenozoic. Dendroctonus currently consists of three highly host-specific lineages that have pinaceous hosts: a basal monospecific clade on Pinoideae (Pinus) and two sister clades that consist of a speciose clade associated exclusively with Pinoideae and six species that breed overwhelmingly in Piceoideae (Picea) and Laricoideae (Pseudotsuga and Larix). The middle Eocene engraving in L. altoborealis represents an early member of Dendroctonus that is ancestral to other congeneric species that colonized a short-bracted species of Larix. This fossil occurrence, buttressed by recent data on the phylogeny of Pinaceae subfamilies and Dendroctonus species, indicates that there was phylogenetically congruent colonization by these bark-beetle lineages of a Pinoideae + (Piceoideae + Laricoideae) host-plant sequence. Based on all available evidence, an hypothesis of a geochronologically early invasion during the Early Cretaceous is supported over an alternative view of late Cenozoic cladogenesis by bark beetles onto the Pinaceae. These data also suggest that host-plant chemistry may be an effective species barrier to colonization by some bark-beetle taxa over geologically long time scales.     

Propagule pressure as a driver of establishment success in deliberately introduced exotic species: fact or artefact?

A central paradigm in invasion biology is that more releases of higher numbers of individuals increase the likelihood that an exotic population successfully establishes and persists. Recently, however, it has been suggested that, in cases where the data are sourced from historical records of purposefully released species, the direction of causality is reversed, and that initial success leads to higher numbers being released. Here, we explore the implications of this alternative hypothesis, and derive six a priori predictions from it. We test these predictions using data on Acclimatization Society introductions of passerine bird species to New Zealand, which have previously been used to support both hypotheses for the direction of causality. All our predictions are falsified. This study reaffirms that the conventional paradigm in invasion biology is indeed the correct one for New Zealand passerine bird introductions, for which numbers released determine establishment success. Our predictions are not restricted to this fauna, however, and we keenly anticipate their application to other suitable datasets.     

Schistocephalus solidus: establishment of tapeworms in sticklebacks--fast food or fast lane?

The penetration of the intestinal mucosal wall is supposed to be critical for helminth parasite infestation, but has rarely been analyzed in detail. We here studied the establishment process of Schistocephalus solidus tapeworms in their second intermediate host, the three-spined stickleback, from oral uptake after experimental exposure, to passage through the gastro-intestinal tract and arrival in the fish body cavity. Using histological techniques, we found tapeworms to penetrate the intestine within 14-24 h, spending most of the time in the stomach lumen and only a very short period in the intestine. Unexpectedly, tapeworms lost their outer layer, together with the cercomer, in the intestine lumen rather than later during intestine wall penetration. Once exposed, the underlying tegument with microtriches might serve to facilitate migration of the parasite into the body cavity.     

Muslim community organizations – sites of active citizenship or self-segregation?

Ethno-religious community organizations in Western countries have often been described as being disconnected from mainstream society, and Muslim community groups have been a special focus of such critique. This article offers a counter-narrative to these widespread allegations. It draws on a synthesis of emerging research on the citizenship-enhancing effects of mosque involvement and on an explorative study involving thirty in-depth interviews with civically active Muslims in Australia and Germany. The article examines the potential of Muslim community organizations to mobilize their member into performing their citizenship through civic and political participation. It offers empirical evidence that many Muslim community organizations, rather than promoting social segregation, act as accessible entry point for Muslims’ civic participation, facilitate cross-community engagement and provide gateways to political involvement. These civic potentials of Muslim community organization have remained underestimated in the public and political discourse on cohesive societies and healthy democracies.     

Comment on Altaba (2015): a case of species misidentification?

Previously in this journal, Altaba (2015) presented an original hypothesis on the dispersal of small wetland snails in Central Europe after the Last Glacial Maximum, based on the discovery of rare species of the genus Vallonia at the foot of the Devín Hill (Slovakia). On the basis of the evidence available to us, it is our opinion that the existence of Vallonia declivis, Vallonia suevica, Vallonia enniensis, and Vallonia tenuilabris at Devín Gate has not been established, and that the hypothesis advanced in Altaba (2015) is therefore unsubstantiated by hard evidence.     

Is the bark of shining gum (Eucalyptus nitens) a sun or a shade leaf?

Photoinhibition and pigment composition of green stem tissues of field-grown adult Eucalyptus nitens were measured on clear spring days with low morning temperatures—conditions that cause photoinhibition in leaves of many plant species. The sun-exposed (north-facing) bark contained less chlorophyll a+b (531 vs 748 mol m^–2), neoxanthin (29 vs 41), and -carotene (54 vs 73), more xanthophyll cycle pigments per unit surface area and per unit chlorophyll (71 vs 53 mol m^–2 and 141 vs 66 mmol mol^–1 chlorophyll), and less lutein per unit chlorophyll (239 vs 190) than the shaded (southern) side. Maximum electron flow rates were 60 mol m^–2 s^–1 on the sun-exposed side, and about 10 mol m^–2 s^–1 on the shaded side. F_v/F_m was always lower than 0.8 on the sun-exposed side and the de-epoxidation state (DEPS) of the xanthophyll cycle was dominated by zeaxanthin in midday samples. F_v/F_m increased quickly after darkening, but DEPS recovered more slowly to 40% overnight. This suggested that rapidly reversible pH-dependent quenching was responsible for the bulk of changes in PS II efficiency. F_v/F_m remained below 0.8 overnight, which may well be indicative of photo-damage to PSII. In contrast, DEPS of the shaded side was lower, and F_v/F_m was higher, than for the sun-exposed side. We conclude that E. nitens chlorenchyma on the sun-exposed stem side has a photosynthetic pigment composition similar to sun leaves and it experiences significant photoinhibition in the field.     

Inverse acyl phosph(on)ates: substrates or inhibitors of beta-lactam-recognizing enzymes?

Acyl phosph(on)ates represent a new class of inhibitors of beta-lactam-recognizing enzymes. Previously described members of this class were aroyl phosph(on)ates. These compounds have been shown to acylate and/or phosphylate the active site serine residue, leading to either transient or essentially irreversible inhibition [Li, N., and Pratt, R. F. (1998) J. Am. Chem. Soc.120, 4264-4268]. The present paper describes the synthesis and evaluation as inhibitors of an inverse pair of acyl phosph(on)ates that incorporate the amido side chain that represents a major substrate specificity determinant of these enzymes. Thus, N-(phenylacetyl)glycyl phenyl phosphate and benzoyl N-(benzyloxycarbonyl)aminomethyl phosphonate were prepared. The former of these compounds was found to be a substrate of typical class A and C beta-lactamases and of the DD-peptidase of Streptomyces R61; it thus acylates the active site serine. In contrast, the latter compound was an irreversible inhibitor of the above enzymes, probably by phosphonylation of the active site serine. With each of these enzymes therefore, the amido side chain rather than the acyl group dictates the orientation of the bound phosph(on)ate and thus the mode of reaction.     

Gating or switching? Gating is a better model of prospective timing (a response to 'switching or gating?' by Lejeune)

Lejeune (1998) (Switching or gating? The attentional challenge in cognitive models of psychological time. Behav. Process. 44, 127-45) analyzed and compared two models of prospective timing: the classical switching model and the attentional-gate model. Lejeune argued that a modified switch notion, which can be opened and closed in a frequency which reflects the amount of attentional resources allocated for timing can provide a satisfactory explanation for the impact of attention on prospective timing, and therefore the notion of an 'attentional switch' is favored over adding an 'attentional gate.' In the present analysis, the two competing models are compared in terms of correspondence with the nature of attentional processes, as well as in terms of logical analysis and explanatory power. Based on this comparison, it is argued that gating is a better model of prospective timing than switching.     

Can genetic data confirm or refute historical records? The island invasion of the small Indian mongoose (Herpestes auropunctatus)

Many studies aimed at reconstructing the invasion history of a species rely, in part, on inferences based on patterns of genetic variation. These inferences warrant careful interpretation, however. In particular, given the time scale of most invasions, the typical demography of invasive species in their invaded range, and the available molecular tools, the underlying assumptions of population genetic models will often be violated. Given this fact, we examined the potential of population genetic data for reconstructing the history of serial introductions of the small Indian mongoose, Herpestes auropunctatus. We used simulations to test the power of existing microsatellite data for testing the credibility of historical introduction records. Although our results are generally consistent with most historical records for H. auropunctatus, the existing data have low power to reject alternative historical hypotheses. Simulations of a wide range of founder population sizes show broadly overlapping results, making rather different historical scenarios of introductions difficult to rule out with typical datasets. We advocate caution in the use of molecular population genetics to infer the history of invasive species, and we suggest extensive simulations as a tool to evaluate, in advance, this approach for addressing important research questions.     

Do biodiversity and human impact influence the introduction or establishment of alien mammals?

What determines the number of alien species in a given region? ‘Native biodiversity’ and ‘human impact’ are typical answers to this question. Indeed, studies comparing different regions have frequently found positive relationships between number of alien species and measures of both native biodiversity (e.g. the number of native species) and human impact (e.g. human population). These relationships are typically explained by biotic acceptance or resistance, i.e. by influence of native biodiversity and human impact on the second step of the invasion process, establishment. The first step of the invasion process, introduction, has often been ignored. Here we investigate whether relationships between number of alien mammals and native biodiversity or human impact in 43 European countries are mainly shaped by differences in number of introduced mammals or establishment success. Our results suggest that correlation between number of native and established mammals is spurious, as it is simply explainable by the fact that both quantities are linked to country area. We also demonstrate that countries with higher human impact host more alien mammals than other countries because they received more introductions than other countries. Differences in number of alien mammals cannot be explained by differences in establishment success. Our findings highlight importance of human activities and question, at least for mammals in Europe, importance of biotic acceptance and resistance.     

Effects of laboratory colonization on Bactrocera dorsalis (Diptera,Tephritidae) mating behaviour: ‘what a difference a year makes’

Laboratory-reared insects are widely known to have significantly reduced genetic diversity in comparison to wild populations; however, subtle behavioural changes between laboratory-adapted and wild or ‘wildish’ (i.e., within one or very few generations of field collected material) populations are less well understood. Quantifying alterations in behaviour, particularly sexual, in laboratory-adapted insects is important for mass-reared insects for use in pest management strategies, especially those that have a sterile insect technique component. We report subtle changes in sexual behaviour between ‘wildish’ Bactrocera dorsalis flies (F1 and F2) from central and southern Thailand and the same colonies 12 months later when at six generations from wild. Mating compatibility tests were undertaken under standardised semi-natural conditions, with number of homo/heterotypic couples and mating location in field cages analysed via compatibility indices. Central and southern populations of Bactrocera dorsalis displayed positive assortative mating in the 2010 trials but mated randomly in the 2011 trials. ‘Wildish’ southern Thailand males mated significantly earlier than central Thailand males in 2010; this difference was considerably reduced in 2011, yet homotypic couples from southern Thailand still formed significantly earlier than all other couple combinations. There was no significant difference in couple location in 2010; however, couple location significantly differed among pair types in 2011 with those involving southern Thailand females occurring significantly more often on the tree relative to those with central Thailand females. Relative participation also changed with time, with more southern Thailand females forming couples relative to central Thailand females in 2010; this difference was considerably decreased by 2011. These results reveal how subtle changes in sexual behaviour, as driven by laboratory rearing conditions, may significantly influence mating behaviour between laboratory-adapted and recently colonised tephritid fruit flies over a relatively short period of time.