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Abstract: The phenologies of introduced relative to native species can greatly influence the degree and symmetry of competition between them. The European spider Linyphia triangularis (Clerck, 1757) (Linyphiidae) reaches very [...]

Invasive spiders pose potential threats to native spiders. In 2002, the European spider Linyphia triangularis (Clerck, 1757) (Araneae: Linyphiidae) was discovered in all but one county in Maine. At Acadia National Park, we conducted a 4-year study of L. triangularis and three native linyphiid species of a similar size (Frontinella communis (Hentz, 1850), Pityohyphantes subarcticus Chamberlin and Ivie, 1943, and Neriene radiata (Walckenaer, 1842)). Using line-transect surveys, we measured population densities in coastal and forest habitat. The density of L. triangularis varied across years but was always significantly higher on the coast than in the forest. In contrast, only one native species was present on the coast and at very low numbers. Coastal L. triangularis were larger and in better condition than those in the forest, and numbers and biomass of insect prey were also higher on the coast. In 2 years, we also conducted transects at a second coastal location in Maine where the invader was at low density. At that site, native densities were substantially higher than at either Acadia site. Our data are consistent with the hypothesis that L. triangularis is reducing populations of native spiders. Companion studies suggest that L. triangularis negatively impacts natives by usurping both web sites and webs. Les araignees envahissantes representent des menaces potentielles pour les araignees indigenes. En 2002, l'araignee europeenne Linyphia triangularis (Clerck, 1757) (Araneae : Linyphiidae) a ete retrouvee dans tous les comtes du Maine, sauf un. Au parc national d'Acadia, nous avons mene une etude de quatre ans de L. triangularis et de trois especes indigenes de linyphiides de taille semblable (Frontinella communis (Hentz, 1850), Pityohypanthes subarcticus Chamberlin et Ivie, 1943 et Neriene radiata (Walckenaer, 1842)). Des inventaires par transect lineaire nous ont servi a mesurer les densites des populations dans les habitats cotiers et forestiers. La densite de L. triangularis varie d'une annee a l'autre, mais elle est toujours significativement plus elevee sur la cote qu'en foret. En revanche, une seule espece indigene est presente sur la cote, mais en tres faible densite. Les L. triangularis de la cote sont plus grands et en meilleure condition que ceux de la foret; les densites et les biomasses des insectes proies sont aussi plus elevees sur la cote. Pendant deux ans, nous avons aussi fait des transects dans un second site cotier dans le Maine dans lequel l'envahisseur a une faible densite. A ce site, les densites des especes indigenes sont plus fortes que dans les deux sites d'Acadia. Nos donnees sont compatibles avec l'hypothese qui veut que L. triangularis reduise les populations d'araignees indigenes. D'autres etudes faites en parallele indiquent que L. triangularis affecte negativement les araignees indigenes en usurpant a la fois leurs toiles et leurs sites de deploiement des toiles. [Traduit par la Redaction], Introduction Invasive arthropod generalist predators have complex and unpredictable effects on native ecosystems (reviewed in Snyder and Evans 2006). In addition to consuming native prey species, invasive predators can harm [...]

Colias eurytheme and C. philodice are sister species with broad sympatry in North America. They hybridize frequently and likely share a significant portion of their genomes through introgression. Both taxa have been ecologically well characterized and exploited to address a broad spectrum of evolutionary issues. Using AFLP markers, we constructed the first linkage map of Colias butterflies. The map is composed of 452 markers spanning 2541.7 cM distributed over 51 linkage groups (40 major groups and 11 small groups with 2-4 markers). Statistical tests indicate that these AFLP markers tend to cluster over the map, with the coefficient of variation of interval sizes being 1.236 (95% C.I. is 1.234-1.240). This nonrandom marker distribution can account for the nonequivalence between the number of linkage groups and the actual haploid chromosome number (N = 31). This study presents the initial step for further marker-assisted research on Colias butterflies, including QTL and introgression analyses. Further investigation of the genomes will help us understand better the roles of introgression and natural selection in the evolution of hybridizing species and devise more appropriate strategies to control these pests.

A study has been conducted to examine mating behavior in two species of the aquatic snails, Viviparus ater and Viviparus contectus, using assortative mating techniques. Heretospecific mating had higher mating propensities than random mating when it was under low density, but nearly equal when under high density. This suggests that mating occurs in conjunction with the fitness of the hybrids in populations.

The mating system of Gammarus pulex is simulated by taking into account the natural pairing behavior. Results show that fine-scaled habitat structure is the dominant factor in the mating pattern of G. pulex. Moreover, direct male-male competition and variable mobility of different-sized males are secondary, but statistically significant, factors. Lastly, the degree of large-male advantage is also affected by habitat structure.