摘要:

The hybrid zone between the Greek land snailsAlbinaria hippolyti aphroditeandAlbinaria hippolyti harmoniaruns 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.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01027.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Two subspecies of the grasshopperChorthippus parallelus(Orthoptera; Acrididae) meet and form a hybrid zone in the Pyrenees. Here we investigate whether the subspecies differ in the blend of cuticular hydrocarbons. Such differences may function as chemical signals, being detected via contact chemoreception and used during mate choice as in other insects. Gas chromatography shows that the subspecies have diverged in the composition of their cuticular hydrocarbons. This difference between subspecies exists over and above variation in cuticular hydrocarbons among individual populations. The majority of the difference can be attributed to the relative amounts of a small group of compounds present in the cuticle. The possible consequences of this chemical divergence for mating encounters between the subspecies are discussed.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01028.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

We examined morphological variation among populations of the stream‐dwelling waterstrider,Aquarius remigis.A previous analysis of allozyme variation along a transect from southern Quebec to southern North Carolina revealed two distinct ‘types' ofA. remigis,north and south of a transition zone in southern New York and northern Pennsylvania. To assess the concordance of morphological and allozyme differentiation, adults were sampled from 15 populations along the original transect, as well as 11 additional populations in New York, Connecticut and New Jersey. Eight measurements of leg and body size were taken of preserved individuals. Univariate and multivariate analyses (multiple regression, PCA, discriminant analysis) reveal significant differentiation between northern and southern populations with a transition zone between latitudes 39oand 42onorth. Strong clines within each region and a clear transition between regions support previous suggestions that there are two distinct ‘types' of this species in eastern North America. The transition zone, in morphology coincides with that revealed by the allozyme variation, but extends further south. The covariance of allozyme frequency and morphometric traits suggests that differentiation has occurred through vicariance and secondary contact, and that in this system, cladistic and adaptive differentiation are co

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01029.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The evolution of greater male than female parental care remains poorly understood. In birds it is thought to be related to precocial chicks and small clutch size. This review shows, however, that such role reversal has also evolved in a family with altricial young and relatively large clutch size: coucals (Centropodidae, Cuculiformes). Males perform most nest building, incubation, and feeding of young. As predicted by sexual selection theory, coucals have also reversed sexual size dimorphism, females being larger than males in all 12 species for which size data are available. Most coucals that have been studied are monogamous, but the black coucalCentropus grilliiappears to be polyandrous, and males perform almost all parental care, whereas females show more active advertisement behaviour. In this species, females are about 50% heavier than males. Polyandry in the black coucal seems to be associated with a shift to a habitat with seasonally rich food resources. Difficulties for female coucals of gathering enough resources for producing several clutches of relatively large eggs may favour mainly male parental care. Female sexual competition and resource storage, and male foraging economy, may explain why females are larger. Additional field studies are needed to test these hypotheses; the coucals are of great interest to sexual selection and mating systems theory.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01030.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Despite their taxonomic and ecological diversity, modern bats (Order Chiroptera) are almost exclusively nocturnal. This behaviour is too ubiquitous to be explained by common patterns of temporal variation in availability of their diverse food sources or by the risk of hyperthermia when flying during the day. Other explanations for bat nocturnality include competition and increased predation risk from birds during the day. In the early and mid Eocene, the known bat fauna consisted of several insectivorous species of sizes similar to those of the modern European assemblage. This fauna was contemporaneous with several species of predatory birds, including owls (Strigiformes), hawks (Accipitridae), falcons (Falconidae) and rollers (Coraciiformes), which were the same size as modern predators on bats. Predation risk could therefore have been a significant factor preventing the early bats from becoming diurnal. Competition from aerial insectivorous birds, however, was less likely to have been significant for bats during the early Eocene, since very few such groups, mainly small Aegialornithidae, were present, with most of the major groups of aerial insectivores evolving later.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01031.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The taxonomie status of different morphotypes generally ascribed to the species of boring spongeCliona viridisis examined. Morphometric, ecological and genetic differences between two morphotypes living sympatrically on rocky shores of the Ligurian Sea are considered. Morphotype 1 is characterized by small, well separated papillae (α stage), exclusively boring into the crust of coralline algae on the exposed rocky bottoms of the upper sublittoral zone. Morphotype 2 shows bigger papillae, often connected by portions of encrusting tissue (βstage), and is predominantly found boring into organogenic concretions in slightly lighted habitats. Measurements of tylostyles indicate that morphotype 1 has spicules significantly smaller than morphotype 2. Electrophoretic analysis shows that the two morphotypes are fixed for different alleles at all four loci scored, indicating absence of gene flow between the two populations, i.e. they appear to be distinct biological specie

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01032.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Quantitative Ecology. Spatial and Temporal Scaling, by David C. SchneiderFossil Horses. Syskmatics, Paleobiology and Evolution of the Family Equidae, by Bruce MacFaddenEcotoxicobgy in Theory and Practice, by Forbes, V. E.&Forbes, T. L.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01033.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY