Dobzhansky–Muller incompatibilities,dominance drive,and sex‐chromosome introgression at secondary contact zones: A simulation study

Dobzhansky–Muller (DM) incompatibilities involving sex chromosomes have been proposed to account for Haldane's rule (lowered fitness among hybrid offspring of the heterogametic sex) as well as Darwin's corollary (asymmetric fitness costs with respect to the direction of the cross). We performed simulation studies of a hybrid zone to investigate the effects of different types of DM incompatibilities on cline widths and positions of sex‐linked markers. From our simulations, X‐Y incompatibilities generate steep clines for both X‐linked and Y‐linked markers; random effects may produce strong noise in cline center positions when migration is high relative to fitness costs, but X‐ and Y‐centers always coincide strictly. X‐autosome and Y‐autosome incompatibilities also generate steep clines, but systematic shifts in cline centers occur when migration is high relative to selection, as a result of a dominance drive linked to Darwin's corollary. Interestingly, sex‐linked genes always show farther introgression than the associated autosomal genes. We discuss ways of disentangling the potentially confounding effects of sex biases in migration, we compare our results to those of a few documented contact zones, and we stress the need to study independent replicates of the same contact zone.     

Rhinocerotidae (Mammalia,Perissodactyla) from the middle Pleistocene levels of Grotta Romanelli (Lecce,southern Italy)

The rhinoceros remains collected during the past century in the lower levels XII (= K) and XI (= I) of the famous Pleistocene locality of Grotta Romanelli (Lecce, southern Italy) are described and compared in detail for the first time. Some remains are referred to Stephanorhinus sp. and others are assigned here to the late early-middle Pleistocene European species Stephanorhinus hundsheimensis based on several morphological characters. Based on its olivine-bearing texture, the volcanoclastic ash sampled from some rhinoceros bones can be referred to the first phase of the Monte Vulture activity (around 630 ka). The results of the stable isotope analyses suggest that the climate in the lowest levels of Grotta Romanelli could have been more arid than it was at the time of the upper level IX, which is generally referred to the late Pleistocene. In addition, both recent day δ¹⁸O_ppt values and MAT are very similar to values calculated for levels X and XII, suggesting that the climate at those times may have been close to the Present one, whereas climate in level IX may have been somewhat cooler. The presence of Stephanorhinus hundsheimensis suggests a middle Pleistocene age for the lower levels of Grotta Romanelli, in agreement with the results obtained from the volcanoclastic material.     

Effects of Host Interspecific Interaction in the <Emphasis Type="Italic">Maculinea</Emphasis>–<Emphasis Type="Italic">Myrmica</Emphasis> Parasite–Host System

A model of interspecific host competition in a system with one parasite (butterfly—Maculinea) and multiple potential hosts (ants—Myrmica) is presented. Results indicate that host interspecific competition increases the occurrence of multiple host behaviour in Maculinea natural populations but decreases the ability of the parasite populations to adapt to the most abundant host species. These qualitative predictions were compared with data on host specificity, with good agreement. Analysis of the data also indicates that Maculinea teleius and Maculinea arion respond differently to changes in relative host abundances. Maculinea teleius shows a larger fraction of sites where it displays multiple host behaviour and a larger fraction of sites where the niches of the hosts overlap. In some instances, Maculinea teleius is adapted to Myrmica hosts that are present in lower frequencies. Maculinea arion is locally more host-specific and occurs at sites where host interspecific competition is unlikely and is more frequently adapted to the most abundant host species.     

Herbarium specimens show patterns of fruiting phenology in native and invasive plant species across New England

Premise of the Study

Patterns of fruiting phenology in temperate ecosystems are poorly understood, despite the ecological importance of fruiting for animal nutrition and seed dispersal. Herbarium specimens represent an under‐utilized resource for investigating geographical and climatic factors affecting fruiting times within species, patterns in fruiting times among species, and differences between native and non‐native invasive species.

Methods

We examined over 15,000 herbarium specimens, collected and housed across New England, and found 3159 specimens with ripe fruits, collected from 1849–2013. We examined patterns in fruiting phenology among 37 native and 18 invasive woody plant species common to New England. We compared fruiting dates between native and invasive species, and analyzed how fruiting phenology varies with temperature, space, and time.

Key Results

Spring temperature and year explained a small but significant amount of the variation in fruiting dates. Accounting for the moderate phylogenetic signal in fruiting phenology, invasive species fruited 26 days later on average than native species, with significantly greater standard deviations.

Conclusions

Herbarium specimens can be used to detect patterns in fruiting times among species. However, the amount of intraspecific variation in fruiting times explained by temporal, geographic, and climatic predictors is small, due to a combination of low temporal resolution of fruiting specimens and the protracted nature of fruiting. Later fruiting times in invasive species, combined with delays in autumn bird migrations in New England, may increase the likelihood that migratory birds will consume and disperse invasive seeds in New England later into the year.