摘要:

The expression of sexuality, overall sex ratio and variation in sex ratio with age of 14 southern Chinese freshwater, brackish and marine bivalves have been investigated.Freshwater species are often hermaphroditic and brooding, e.g.MusculiumandPisidium(Pisidiidae), whileCorbicula fluminea(Corbiculidae) demonstrates wide intraspecific variability in sexual expression, but also broods.Anodontu woodiunu(Unionidae) andLimnoperna fortunei(Mytilidae) are dioecious, with low incidence of hermaphrodites in the former, but both have strong female‐biased overall sex ratio which does not change with age. Juvenile age classes ofCorbiculacf.fluminalishave female‐biased sex ratio. A pronounced female bias is means to optimize reproductive success, by maximizing resource allocation into more energy‐demanding oogenesis, in temporally and spatially heterogeneous lacustrine habitats. In such habitats, moreover, there are probably diminishing returns to producing sons.Mangrove and brackish water species are all dioecious (exceptSuccostrea cuculluta)with slight male‐biased sex ratio overall, but are strongly male‐biased as juveniles. This strategy similarly optimizes success in fluctuating intertidal environment, where high rates of juvenile mortality may be expected possibly, for example, through enhanced predation. In such case, therefore, the greater investment in sons is prerequisite to an overall balanced sex ratio. The marine intertidal species,Perna ciridis(Mytilidae) andDonax semigranosus(Donacidae) have stable I:I sex ratio, notvvarying with age, and are representative of the ‘typical’ dioecious condition recorded for most marine bivalves.Thus, although intraspecific variations in life history tactics and sexual strategies equip all species for variable environment, it is postulated that permutations of the ‘dioecious’ condition, mediated through variations in the sex ratio either overall or with age, broadly equip the Bivalvia for the total range of

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04754.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Gerbillus pyramidumandG. allenbyiare primarily granivorous, nocturnal rodents that are sympatric over many sandy areas of the Negev Desert. However, in their overall distribution,G. pyramidumoccurs in extreme desert areas whereasG. allenbyidoes not. We measured the average daily metabolic rate (ADMR) of gerbils of each species when they were offered pelleted diet. Given the difference in their distribution, we reasoned that the more xericG. pyramidumwould have lower ADMR thanG. allenbyi;however, given the similarity in their diets, we reasoned that their ADMRs would be similar. The latter alternative was supported. ADMR ofG. pyramidum(body mass = 31·9 ± 5·4 g) was 427·1 kJ·kg−0.75·d−1, 58% of that predicted for a rodent of its body mass; whereas ADMR ofG. allenbyi(body mass = 22·3±2·3 g) was 387·7 kJ·kg−0.75·d−1, 49%) of that predicted. On the basis of these results, we suggest that factors other than their ADMRs are important in determining their geogra

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04755.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The taxonomy of Arabian gazelles has been confused by single specimen collected from the Farasan Islands in the Red Sea in the 1820s. There is still population of gazelles on the islands. They form distinct taxon most closely related to the mountain gazelleGazella gaiella, which is characterized by small size, grey‐brown colouring, very short horns in the female and rounded upper tooth‐row in the male. This gazelle bears no resemblance to the type specimen ofG. arabica, said to come from the Farasan Islands. In this paper the Farasan gazelle is described asGazella gazella Jarasanin.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04756.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The intraspecific behaviour of the communal‐territorial spitting spider,Scytodes fusca, from North Queensland, Australia, is described from laboratory observations. This spider is tolerant of most conspecific intruders on the web but adults, particularly females, do display aggression to other adults by charging, chasing and spitting. During courtship, both the male and the female tap on the web. Courtship inS. fuscais similar to that of a non‐social scytodidScytodes thoracica.Males often stay with the female for a time after mating. Adults appear to be more cannibalistic toward third than toward first and second instar juveniles, This finding is discussed in relation to the mechanisms of intraspecific recognition. The social behaviour ofS. fuscais compared with that of other scytodids and the possible evolution of sociality inS. fuscafrom the parent offspring association is discus

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04757.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY