Irma Wynhoff

Differences in the climatic debts of birds and butterflies at a continental scale

Climate changes have profound effects on the distribution of numerous plant and animal species(1-3). However, whether and how different taxonomic groups are able to track climate changes at large spatial scales is still unclear. Here, we measure and compare the climatic debt accumulated by bird and butterfly communities at a European scale over two decades (1990-2008). We quantified the yearly change in community composition in response to climate change for 9,490 bird and 2,130 butterfly communities distributed across Europe(4). We show that changes in community composition are rapid but different between birds and butterflies and equivalent to a 37 and 114 km northward shift in bird and butterfly communities, respectively. We further found that, during the same period, the northward shift in temperature in Europe was even faster, so that the climatic debts of birds and butterflies correspond to a 212 and 135 km lag behind climate. Our results indicate both that birds and butterflies do not keep up with temperature increase and the accumulation of different climatic debts for these groups at national and continental scales.

Does the presence of ant nests matter for oviposition to a specialized myrmecophilous Maculinea butterfly

More than 50% of the lycaenid butterflies have an ant–associated lifestyle (myrmecophily) which may vary from coexistence to specific mutualistic or even parasitic interactions. Ant–related host–plant selection and oviposition has been observed in some myrmecophilous lycaenids. Therefore, it is remarkable that there is no evidence for this behaviour in the highly specialized, obligate myrmecophilous butterflies of the genus Maculinea. In contrast with previous findings, our results provide evidence for ant–related oviposition patterns in Maculinea alcon in relation to the distribution of specific host–ant nests (i.e.Myrmica ruginodis) based on repeated egg counts during the flight period in two populations. We also show that ant–related oviposition can be counterbalanced by intraspecific competition and oviposition deterrency when host plants already carry several eggs. Therefore, the absence of a correlation between egg load and the presence of host–ant nests at the end of the flight period should be interpreted carefully. Whether ovipositional cues are obtained either directly (from ants or their nests) or indirectly (from vegetation structure), and whether alternative explanations based on the phenology and growth form of host plants are possible, is discussed.

REVIEW: The recent distribution of the European Maculinea species

The genus Maculinea is confined to the Palaearctic region. Four species occur from Central Europe to China and/or Japan, while M. rebeli is probably restricted to Europe. Although within many Western European countries the distribution of the species is well known, there are still many questions. The exact status of some of the species is still unclear and the amount of decline in this century is unknown. In Asia, especially within the nations of the former USSR, the distributions of species are even less well known and as a basis for good research and effective nature conservation, knowledge on these subjects is needed.

Looking for the ants: selection of oviposition sites by two myrmecophilous butterfly species

Abstract Obligate myrmecophilous butterfl y species, such as Maculinea teleius and M. nausithous that hibernate as caterpillar in nests of the ant species Myrmica scabrinodis and M. rubra r espectively, have narrowly defi ned habitat requirements. One would expect that these butterfl ies are able to select for sites that meet all their requirements. Both butterfl y species occur in habitats where their initial larval resource, the host plant Sanguisorba offi cinalis, is abundant, while the ant nests ar e relatively less abundant. With ants in the prox-imity of a host plant, caterpillars have a chance of being found by their host ant species, while the host plant could become a sink as caterpillars will die when there are no ants close to the host plant. We tested whether females oviposit on host plants in the close proximity of host ants (ant-mediated oviposition) or whether there is random oviposition, using 587 1-m 2 plots in and around a nature reserve in Th e Netherlands where both species were reintroduced. We found that females of both species indeed more often deposit eggs on host plants nearby ants than on host plants without ants. Visits of adult butterfl ies to plots with the host plant but without the host ants only occurred in years with high butterfl y densities. We argue that understanding site selection for oviposition is important for these highly endangered butterfl y species with a specialised life cycle, especially after disturbances or reintroductions.

Phengaris (Maculinea) alcon butterflies deposit their eggs on tall plants with many large buds in the vicinity of Myrmica ants

The survival of eggs and larvae is dependent on the oviposition site selection of their mothers. In obligate myrmecophilic butterflies, both host plant phenology and host ant presence are expected to affect the decision where to deposit eggs. The importance of ant nest presence in the oviposition site selection of Phengaris butterflies is, however, highly debated. We studied oviposition in the largest Phengaris (Maculinea) alcon population in Portugal, exploiting Gentiana pneumonanthe as the host plant and Myrmica aloba as host ant. We collected phenological plant data and recorded the presence and number of eggs on plants with and without Myrmica ants nearby during the flight period of the butterfly. Females oviposited on tall plants with many tall buds, while the presence of host ant nests weakly affected oviposition on plants where the probability of finding ants at close range was high. Moreover, larger plants with many tall buds close to host ant nests received more eggs. A density‐dependent shift in oviposition was not found as the proportion of buds not infected with eggs did not differ between plants with or without ants, whereas plant characteristics did have an effect. Tall plants with many large buds were associated with earlier oviposition. Our results suggest that females of P. alcon in Portugal choose gentian plants for oviposition mainly based on plant characteristics whereas the vicinity of ants had a weak effect. Moreover, our study shows that testing the ant‐mediated oviposition hypothesis requires baiting ants more than once.

Maculinea alcon exploits Myrmica aloba in Portugal: unusual host ant species of a myrmecophilous butterfly in a peripheral region

Larvae of the obligate myrmecophilous social parasite Maculinea alcon (Lepidoptera: Lycaenidae) were found exclusively using Myrmica aloba (Hymenoptera: Formicidae) ant hosts in NE-Portugal. This is the first record of the host ant usage of any Maculinea species in Portugal, and of any Maculinea using M. aloba nests. These results on such peripheral European populations confirm that knowledge of the local host ant species is crucial for the successful protection of these endangered butterflies, and vital for examining the evolution of such interactions.

Resource use of specialist butterflies in agricultural landscapes: conservation lessons from the butterfly Phengaris (Maculinea) nausithous

Most of the European grassland butterfly species are dependent on species rich grasslands shaped by low intensity farming. Conservation of these specialist species in agricultural landscapes relies on knowledge of their essential resources and the spatial distribution of these resources. In The Netherlands, the dusky large blue Phengaris (Maculinea) nausithous butterflies were extinct until their reintroduction in 1990. In addition, a spontaneous recolonization of road verges in an agricultural landscape occurred in 2001 in the southern part of The Netherlands. We analyzed the use of the essential resources, both host plants and host ants, of the latter population during the summers of 2003 and 2005. First we tested whether the distribution of the butterflies during several years could be explained by both the presence of host plants as well as host ants, as we expected that the resource that limits the distribution of this species can differ between locations and over time. We found that oviposition site selection was related to the most abundant resource. While in 2003, site selection was best explained by the presence of the host ant Myrmica scabrinodis, in 2005 it was more strongly related to flowerhead availability of the host plant. We secondly compared the net displacement of individuals between the road verge population and the reintroduced population in the Moerputten meadows, since we expected that movement of individuals depends on the structure of their habitat. On the road verges, butterflies moved significantly shorter distances than on meadows, which limits the butterflies in finding their essential resources. Finally we analyzed the availability of the two essential resources in the surroundings of the road verge population. Given the short net displacement distances and the adverse landscape features for long-distance dispersal, this landscape analysis suggests that the Phengaris population at the Posterholt site is trapped on the recently recolonized road verges. These results highlight the importance of assessing the availability of essential resources across different years and locations relative to the movement of the butterflies, and the necessity to careful manage these resources for the conservation of specialist species in agricultural landscapes, such as this butterfly species.

Phengaris (Maculinea) teleius butterflies select host plants close to Myrmica ants for oviposition, but P. nausithous do not

Many lycaenid butterfly species have interactions with ants, with 12% obligatorily depending on two sequential sources of larval food, namely host plants and host ants. When host plants are abundant but the density of host ant nests is relatively low, most host plants have no host ant nest in their vicinity and are thus unsuitable for larval survival. Obligatorily myrmecophilous female butterflies, whose caterpillars feed on ant larvae, would have a comparative advantage if they deposit eggs on host plants in the proximity of a host ant nest. However, this ant‐mediated oviposition has been hotly debated. In an open‐air insectory experiment, we tested whether oviposition is ant‐mediated or not for two obligatory myrmecophilous butterfly species, Phengaris (Maculinea) nausithous Bergsträsser and Phengaris teleius Bergsträsser (Lepidoptera: Lycaenidae). Female butterflies could select host plants close to either no ant nest or a nest of one of the two Myrmica species (Hymenoptera: Formicidae) that are thought to be their host ant. Our results support ant‐mediated oviposition in P. teleius, but also indicate that there is no preference for either of the Myrmica species. More eggs were deposited and more caterpillars were found on long flowerheads close to Myrmica ant nests than on those without nests. Our findings suggest that ant presence is more important than flowerhead phenology for females of P. teleius. In contrast, P. nausithous females were not attracted by ants but preferred long flowerheads with a low percentage of green coloration. With these findings, this study contributes to better understanding of the habitat requirements of two highly specialized butterfly species.