Predicting adaptation of phenology in response to climate change, an insect herbivore example

Climate change has led to an advance in phenology in many species. Synchrony in phenology between different species within a food chain may be disrupted if an increase in temperature affects the phenology of the different species differently, as is the case in the winter moth egg hatch–oak bud burst system. Operophtera brumata (winter moth) egg hatch date has advanced more than Quercus robur (pedunculate oak) bud burst date over the past two decades. Disrupted synchrony will lead to selection, and a response in phenology to this selection may lead to species genetically adapting to their changing environment. However, a prerequisite for such genetic change is that there is sufficient genetic variation and severe enough fitness consequences. So far, examples of observed genetic change have been few. Using a half-sib design, we demonstrate here that O. brumata egg-hatching reaction norm is heritable, and that genetic variation exists. Fitness consequences of even a few days difference between egg hatch and tree bud opening are severe, as we experimentally determined. Estimates of genetic variation and of fitness were then combined with a climate scenario to predict the rate and the amount of change in the eggs' response to temperature. We predict a rapid response to selection, leading to a restoration of synchrony of egg hatch with Q. robur bud opening. This study shows that in this case there is a clear potential to adapt – rapidly – to environmental change. The current observed asynchrony is therefore not due to a lack of genetic variation and at present it is unclear what is constraining O. brumata to adapt. This kind of model may be particularly useful in gaining insight in the predicted amount and rate of change due to environmental changes, given a certain genetic variation and selection pressure.     

Climate change leads to decreasing bird migration distances

Global climate change has led to warmer winters in NW Europe, shortening the distance between suitable overwintering areas and the breeding areas of many bird species. Here we show that winter recovery distances have decreased over the past seven decades, for birds ringed during the breeding season in the Netherlands between 1932 and 2004. Of the 24 species included in the analysis, we found in 12 a significant decrease of the distance to the wintering site. Species from dry, open areas shortened their distance the most, species from wet, open areas the least, while woodland species fall in between the other two habitats. The decline in migration distance is likely due to climate change, as migration distances are negatively correlated with the Dutch temperatures in the winter of recovery. With a shorter migration distance, species should be better able to predict the onset of spring at their breeding sites and this could explain the stronger advancement of arrival date found in several short distance species relative to long-distance migrants.     

Parallel phenotypic evolution in a wolf spider radiation on Galápagos

Within island archipelagos, repeated ecological settings may lead to radiations wherein similar niches are recurrently occupied. Although it has been shown that species with common habitat requirements share particular traits, it remains relatively unexplored to what extent this may lead to the repeated evolution of almost identical phenotypes (phenocopies) and how this correlates with traits subjected to sexual selection. Exploring divergence patterns of ecological and sexual relevant traits within spiders seem promising to enhance our understanding of the relative role of natural and sexual selection. Here, we conduct a detailed morphological analysis on a large set of genital and non‐genital traits (morphometrics, colour pattern) within a radiation of the wolf spider genus Hogna Simon, 1885 on Galápagos and interpret these data, taking into account their known phylogenetic relationship. Our results show that recurrent environmental gradients have led to the parallel evolution of almost identical phenotypes, which not only proves that natural selection has driven morphological divergence, but also suggests that a similar genetic or developmental basis most likely underlies this divergence. Among‐species variation in genital traits in contrast rather reflects the phylogenetic relationships on Santa Cruz and San Cristóbal. The combination of these data indicate that speciation in this system is driven by the combined effect of ecological mechanisms and allopatric divergence in sexual traits. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 123–136.     

Using space‐for‐time substitution and time sequence approaches in invasion ecology

1. Invasion biologists use two main approaches to evaluate the effects of non‐native species (NNS) on diversity of native species (DNS), namely space‐for‐time and time approaches. These approaches have pitfalls related to lack of controls: the former lacks pre‐invasion data, while the latter often lacks data from non‐invaded sites. 2. We propose a framework that combines space‐for‐time and time approaches and which should result in more focused mechanistic hypotheses and experiments to test the causes of invasibility and the effects of NNS on DNS. We illustrate the usefulness of our framework using two case studies: one with the submersed macrophyte, Hydrilla verticillata, in reservoir and the other with the fish, Geophagus proximus, in a large river–floodplain system. 3. Hydrilla verticillata invaded sites with DNS similar to that found in non‐invaded sites, indicating that biotic and/or abiotic factors did not influence invasion success; however, DNS increased over time in invaded sites compared with non‐invaded sites, suggesting that H. verticillata facilitated natives. In contrast, G. proximus invaded sites with higher DNS than non‐invaded sites, suggesting that biotic and/or abiotic factors favouring natives were important for invasion success, but DNS increased in invaded and non‐invaded sites over time, indicating that an independent factor contributed to DNS increases. 4. Conclusions from both studies would have been inaccurate or incomplete if the space‐for‐time and time approaches had not been used in combination as proposed in our framework.     

Life on the edge: a hybrid zone in AZbinaria hippolyti (Gastropoda: Clausiliidae) from Crete

The hybrid zone between the Greek land snails Albinaria hippolyti aphrodite and Albinaria hippolyti harmonia runs exactly along the edge of a gorge. At two localities, we analysed patterns of variation in three enzyme loci, six conchological characters, and two anatomical characters across the zone. Clines in the various characters are largely coincident and concordant. They are narrow (approximately 30 m wide) where the ecological transition is abrupt, and wider (approximately 120 m wide) where a valley cuts into the gorge, making the environmental change more gradual. In spite of the obvious correlation with an ecological transition, we do not believe the zone is maintained by a selection gradient. Instead, direct and indirect evidence for hybrid disadvantage and evidence for directional dispersal at the edge of the gorge suggest that it is a tension zone, held at the ecotone by differential dispersal of at least one of the parental types. We speculate on the possibility that reinforcement may act in the hybrid zone. Our data on dispersal and reproductive isolating mechanisms lead us to believe that reinforcement may only be possible at localities where the hybrid zone is very narrow.     

Food plant and herbivore host species affect the outcome of intrinsic competition among parasitoid larvae

1. In nature, several parasitoid species often exploit the same stages of a common herbivore host species and are able to coexist despite competitive interactions amongst them. Less is known about the direct effects of resource quality on intrinsic interactions between immature parasitoid stages. The present study is based on the hypothesis that variation in the quality or type of plant resources on which the parasitoids indirectly develop may be complementary and thus facilitate niche segregation favouring different parasitoids in intrinsic competition under different dietary regimes. 2. The present study investigated whether two herbivore species, the cabbage butterflies Pieris brassicae and Pieris rapae (Pieridae), and the quality of two important food plants, Brassica oleracea and Brassica nigra (Brassicaceae), affect the outcome of intrinsic competition between their primary larval endoparasitoids, the gregarious Cotesia glomerata (Braconidae) and the solitary Hyposoter ebeninus (Ichneumonidae). 3. Hyposoter ebeninus is generally an intrinsically superior competitor over C. glomerata. However, C. glomerata survived more antagonistic encounters with H. ebeninus when both developed in P. brassicae rather than in P. rapae caterpillars, and while its host was feeding on B. nigra rather than B. oleracea. Moreover, H. ebeninus benefitted from competition by its higher survival in multiparasitised hosts. 4. These results show that both plant and herbivore species mediate the battleground on which competitive interactions between parasitoids are played out and may affect the outcomes of these interactions in ways that enable parasitoids to segregate their niches. This in turn may promote coexistence among parasitoid species that are associated with the same herbivore host.