Egg production and viability in the copepod Temora stylifera (collected in the Bay of Naples, Italy in 1992) were strongly dependent on food type. A flagellate (Isochrysis galbana) diet induced the production of good quality eggs that developed to hatching. By contrast, two diatoms (Chaetoceros curvisetum, Phaeodactylum tricornutum) resulted in poor egg quality, with hatching success as low as 20% of total egg production. With the third diatom tested, Skeletonema costatum, females produced eggs for only 3 to 4 d, after which time they either became sterile or died. These results are discussed in relation to previous findings regarding the impact of the dinoflagellate Prorocentrum minimum and the diatom Thalassiosira rotula on the hatching success of T. stylifera eggs. Low egg viability was possibly not due to an absence of remating or a deficiency of some specific essential nutrient required for egg development but to the presence of inhibitory compounds blocking cell division during early copepod embryogenesis. This questions the traditional view that diatoms are an important food item regulating copepod secondary production.
Viviparity in squamate reptiles is presumed to evolve in cold climates by selection for increasingly longer periods of egg retention. Longer periods of egg retention may require modifications to other reproductive features associated with the evolution of viviparity, including a reduction in eggshell thickness and clutch size. Field studies on the thermal and reproductive biology of high (HE) and low (LE) elevation populations of the oviparous lizard, Sceloporus scalaris, support these expectations. Both day and night-time temperatures at the HE site were considerably cooler than at the LE site, and the activity period was 2 h shorter at the HE than at the LE site. The median body temperature of active HE females was 2°C lower than that of LE females. HE females initiated reproduction earlier in the spring than LE females, apparently in order to compensate for relatively low temperatures during gestation. HE females retained eggs for about 20 days longer than LE females, which was reflected by differences in the degree of embryonic development at the time of oviposition (stages 35.5-37.0 versus stages 31.0-33.5, respectively). These results support the hypotheses that evolution of viviparity is a gradual process, and is favored in cold climates. Females in the HE population exhibited other traits consistent with presumed intermediate stages in the evolution of viviparity; mean eggshell thickness of HE eggs (19.3 μm) was significantly thinner than that of LE eggs (26.6 μm) and the size-adjusted clutch sizes of HE females (9.4) were smaller than those of LE females (11.2).
We examined the influence of body mass in early winter on litter size, growth and sex ratio of young, as well as the influence of gestation and lactation on overwinter loss of mass among female black bears (Ursus americanus) in La Mauricie National Park, Quebec, Canada. All adult females weighing greater than or equal to 77 kg gave birth and no female reproduced when weighing <56 kg. Litter size (two to four young) was influenced by maternal condition in early winter, and overwinter loss of mass greater for females producing litters of three and four young. For a particular litter size, heavier females tended to produce more male young than expected from an equal sex ratio. Maternal condition, however, could not explain the strongly male-biased sex ratio (2.5 males:1.0 female) at birth observed in this population. Significance of sex ratio at birth in relation to the regulation of the population of bears at La Mauricie National Park is discussed.
Intracytoplasmic sperm injection (ICSI) was successful in the mouse when a piezo-driven micropipette was used instead of a mechanically driven conventional pipette. Eighty percent of sperm-injected oocytes survived, and approximately 70% of them developed into blastocysts in vitro. When 106 embryos at the 2- to 4-cell stage were transferred to eight naturally mated foster mothers, 30% of the embryos (25-43%, depending on the host) reached the full term. Except for two that were cannibalized soon after birth, all of the young (30 pups) grew into normal adults. Studies of this type on the mouse may increase understanding of the fertilization process and of how ICSI works.
Knowledge of the reproductive biology of endemic plants improves our understanding of how mating system may be related to patterns of species abundance and provides a basis for the development of rational conservation programmes. In this paper we present natural population data on the floral biology and reproductive ecology of the endemic Mediterranean species Cyclamen balearicum Willk. This is a long-lived, diploid perennial herb which occurs in southern France in five fragmented and isolated regions and on the Balearic Islands of Mallorca, Menorca, Ibiza, Cabrera and Draponera. Our observations indicate a particularly scarce pollinator activity (rare syrphid visits) and dispersal by ants over small distances. A controlled pollination experiment in a natural population showed that in southern France C. balearicum is fully self-compatible and that selfing is autonomous and probably delayed (i.e. following opportunities for outcrossing). The proximity of stigmas and anthers will favour autonomous selfing. The high pollen/ovule ratio indicates nevertheless that C. balearicum has a mixed mating system. Patterns of variation in stigma-anther separation and pollen production per newer suggest that not only has the current mating system of the species evolved from an outcrossing ancestor but that due to the fragmentation and isolation of populations greater levels of selfing have evolved in southern France (and to an intermediate degree on Ibiza and Menorca). On the island of Mallorca where larger continuous belts of C. balearicum habitat still exist the species has floral traits indicating a more outcrossed mating system. To our knowledge this is the first paper to document such trends in floral traits in the endemic component of the Mediterranean flora. (C) 1995 The Linnean Society of London