摘要:

Why do females of many species mate with males on the basis of traits apparently detrimental to male survival? The answer may lie in the fact that these male traits are correlated with male condition. We consider the argument that high male condition directly benefits female fecundity and/or viability (e.g. through lower transmission of parasites, improved control of resources, or better paternal care). Using a quantitative genetic model we show how female preferences for male traits that indicate condition can evolve, even if the male traits themselves have deleterious effects on both the male and the female's fecundity. So‐called ‘arbitrary preferences’ can spread in this way because male traits subject to sexual selection are often under additional selection to become correlated with condition. At equilibrium the positive effects of male condition on a female's fecundity and the negative effects of the male trait on her fecundity are balanced and the female preference is under stabilizing selection. The male trait will often be correlated with viability, but not with fecundity, even though the preference evolved as a result of differences in male fecundity. The mean fecundity of females is not maximized, and can steadily decline as the male trait and female preference evolve. If the male trait has no direct deleterious effects on female fecundity, as may happen in species with no paternal care, female preferences are under continuous directional selection to inc

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00887.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

We consider differences between dipteran, hymenopteran and coleopteran parasitoids in the following categories: taxonomic range and developmental stage of hosts attacked; habitats they are attacked in; developmental stage of the parasitoid contacting the host; occurrence of phoresy, and attacking hosts during flight. Using existing phylogenetic classifications we reconstruct possible ancestral conditions to the parasitoid clades in the three orders. By considering these as phylogenetic constraints and potentialities we attempt to account for the observed differences between the parasitoids within the orders.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00888.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

This paper tests four theories of the maintenance of genetic recombination using published chiasma frequencies of 194 plant species representing 15 families of angiosperms. The theories are that recombination is favoured by environmental unpredictability, by fluctuating selection, by mutational load or by sib‐competition. The level of genetic recombination was approximated by recombination index and by the number of excess chiasmata. Both measures were higher in animal‐dispersed than in other species and increased as dispersal distance decreased. This association was found at all taxonomic levels. Chiasma frequency was not associated with life span of the species. Recombination index was lower in perennial than in annual species, but the reverse trend was observed among genera. Number of chiasmata per bivalent tended to decrease as the number of chromosomes increased, but this association was statistically insignificant at all taxonomic levels. No association was found between number of chiasmata per cell and nuclear DNA content.These patterns did not support the theories that environmental unpredictability or fluctuating selection due to parasite pressure favour recombination, and they offered only very little support for the theory that recombination is favoured so that mutational load can be decreased. The only theory that was consistent with the observed data is the sib‐competition theory, which suggests that genetic recombination is maintained so that the intensity of competition with sibs is re

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00889.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The distribution of the 346 hydromedusan species hitherto recorded from the Mediterranean is considered, dividing the species into zoogeographical groups. The consequences for dispersal due to possession or lack of a medusa stage in the life cycle are discussed, and related to actual known distributions. There is contradictory evidence for an influence of life cycle patterns on species distribution. The Mediterranean hydromedusan fauna is composed of 19.5% endemic species. Their origin is debatable. The majority of the remaining Mediterranean species is present in the Atlantic, with various world distributions, and could have entered the Mediterranean from Gibraltar after the Messinian crisis. Only 8.0% of the fauna is classified as Indo‐Pacific, the species being mainly restricted to the eastern basin, some of which have presumably migrated from the Red Sea via the Suez Canal, being then classifiable as Lessepsian migrants. The importance of historical and climatic factors in determining the composition of the Mediterranean fauna of hydromedusae is discusse

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00890.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Populations of the planthopper.Nilaparvata bakeri(Muir) were sampled from the Philippines (Luzon), Indonesia (Bali), India (Bihar) and Sri Lanka (Central Province) from the grassLeersia hexandra(Schwartz), and cultured in Cardiff. Low intensity vibratory signals produced by males and females during mate location and courtship were recorded and analysed. Obvious differences were found between male calling songs of insects from the Philippines and those from the other three areas. Smaller differences were detected between the Indonesian, Indian and Sri Lankan populations. Hybrids between Philippine and Indonesian, and Indonesian and Sri Lankan, insects were obtained freely in the laboratory. Male calls of F, hybrids were variable and intermediate between parentals. Mate choice experiments showed no significant assortative mating between the different populations. There was no indication of reproductive isolation and therefore of different biological species. The assumption that different male calling songs necessarily indicate the presence of different biological species is not confirmed in this example.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1993.tb00891.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY