Differences In Reproductive Traits Research Articles

Influence of continental history on the ecological specialization and macroevolutionary processes in the mammalian assemblage of South America: Differences between small and large mammals

BackgroundThis paper tests Vrba's resource-use hypothesis, which predicts that generalist species have lower specialization and extinction rates than specialists, using the 879 species of South American mammals. We tested several predictions about this hypothesis using the biomic specialization index (BSI) for each species, which is based on its geographical range within different climate-zones. The four predictions tested are: (1) there is a high frequency of species restricted to a single biome, which henceforth are referred to as stenobiomic species, (2) certain clades are more stenobiomic than others, (3) there is a higher proportion of biomic specialists in biomes that underwent through major expansion-contraction alternation due to the glacial-interglacial cycles, (4) certain combinations of inhabited biomes occur more frequently among species than do others.ResultsOur results are consistent with these predictions. (1) We found that 42 % of the species inhabit only one biome. (2) There are more generalists among species of Carnivora than in clades of herbivores. However, Artiodactyla, shows a distribution along the specialization gradient different from the one expected. (3) Biomic specialists are predominant in tropical rainforest and desert biomes. Nevertheless, we found some differences between small and large mammals in relation to these results. Stenobiomic species of micromammalian clades are more abundant in most biomes than expected by chance, while in the case of macromammalian clades stenobiomic species are more frequent than expected in tropical rainforest, tropical deciduous woodland and desert biomes only. (4) The most frequent combinations of inhabited biomes among the South American mammals are those with few biomes, i.e., the ones that suffered a higher rate of vicariance due to climatic cycles.ConclusionOur results agree with the resource-use hypothesis and, therefore, with a major role of the past climatic changes as drivers of mammalian evolution. Nevertheless, deviations from the expectations indicate the importance of differences in reproductive traits and paleobiogeographic history for the macroevolutionary processes involved. In the case of South American mammals, the Pliocene Great American Biotic Interchange strongly influences the ecological characteristics of this assemblage. Furthermore, the Andes have acted as a fertile ground for speciation in environments prone to vicariance. Finally, the micromammals appear as more prone to biomic specialization than larger species. These factors are responsible for some of the differences found between South America and Africa in the studied pattern. For example, the extensive South American mountain ranges favour a higher number of combinations of inhabited biomes in comparison with Africa.

The reproductive strategies in neighbouring populations of the European pond turtle, Emys orbicularis, in central Italy

Two large Emys orbicularis populations of coastal central Italy, from San Rossore and Camp Darby (Tuscany), were studied to test patterns of reproductive biology variability, and life history traits. No significant difference was found between the localities for any of the considered linear measurements (raw data), either of males or females. Despite this, analysis of covariance revealed differences for most of the parameters examined (log‐transformed variable). Females from San Rossore were significantly larger, heavier and longer than those from Camp Darby, and produced a significantly larger clutch than those of Camp Darby (six vs five eggs). Combining radiographic, ultrasonic and manual techniques, it was found that more than 77% of all adult‐sized females reproduced annually and more than 50% of them laid a second clutch during the same season. While egg size did not vary between localities (raw data), analysis of covariance on egg shape (all variables considered together) revealed a significant difference. The observed differences in reproductive traits of these populations are significant and hypothesised to be related to ecological as well as to demographic constraints.

Cohort effects and deer population dynamics

Among-individual variation of life history traits in a given population of deer has most often been accounted for by differences among sex and age classes and by current environmental variation (mostly changes in density and climatic conditions). However, among-individual differences in fitness can also be generated by differences in environmental conditions during the year of birth. Such cohort effects can be divided into two different components. First, among-year differences in environmental conditions at birth may produce large yearly variation in recruitment that generates a direct numerical effect (i.e., a high proportion of newborns are recruited in good years, whereas very low proportions are recruited when environmental conditions encountered by newborns during their first weeks of life are poor). Second, when recruited into the population, individuals born in a good year may reproduce earlier, reach a larger body mass, and have a higher reproductive success than individuals born in a poor year. We call the long-lasting influence on individual fitness of environmental conditions during the year of birth a delayed quality effect. Here, we first review briefly evidence of numerical and quality effects recently accumulated in deer populations. Then, by using long-term monitoring (> 20 y) of two contrasted roe deer (Capreolus capreolus) populations, we assess the influence of the among-cohort differences in reproductive traits, age- and sex-specific survival rates, and population growth rate. Results show that cohort effects (1) are widespread in deer populations and (2) may have a major influence on population dynamics, especially in low-performance populations. Cohort effects should therefore be accounted for in management plans of deer populations.

Reproductive isolation and reproductive output in two sympatric mussel species (Mytilus edulis, M. trossulus) and their hybrids from Newfoundland

The mussels Mytilus edulis L. and M. trossulus Gould are found sympatrically in most areas of Newfoundland, with a low frequency of hybrids. To assess the potential for reproductive isolation, we sampled mussels from three sites in an eastern Newfoundland Bay from May–October 1996 to determine if there were differences in the reproductive cycles of the two species and their natural hybrids. In mussels with sheil lengths of 38–42 mm, males and females with mature gametes were dominant in June for M. edulis and hybrids, while M. trossulus showed a lower frequency of individuals with mature gametes. M. trossulus and hybrids spawned over a prolonged period (from late spring to early autumn) compared with most M. edulis individuals that spawned over a period of 2–3 weeks in July. This asynchrony in spawning activity between the two species may partially explain the low frequency of hybrids found in previous studies of these mussel populations. Female and male hybrids between M. edulis and M. trossulus showed normal gonad development, ripening and spawning, providing an opportunity for the introgression of genes between the two species. M. trossulus had a higher reproductive output than M. edulis of similar shell length, while hybrids showed intermediate values of reproductive output. M. trossulus females produced smaller eggs than either M. edulis or hybrids. Differences in reproductive traits may partially explain the maintenance of the mussel hybrid zone in Newfoundland.

Mechanisms for delayed density‐dependent reproductive traits in field voles, Microtus agrestis: the importance of inherited environmental effects

Reproductive traits of voles vary with the phases of the population density fluctuations. We sought to determine whether the source of this variation resides in the individuals or in their environment. Overwintering field voles (Microtus agrestis) from two cyclic out‐of‐phase populations (increase and peak phases) were sampled in early spring and bred in the laboratory for two generations under standardised conditions with ambient light and temperature. Monitoring of the source populations by capture‐mark‐recapture showed large differences in reproductive performance. In the increase area, reproduction started six weeks earlier, the probability of maturation of young‐of‐the‐year was more than ten times higher during mid‐summer, and reproduction continued nearly two months later in the autumn than in the peak area. These differences were not found to be associated with a difference in age structure of overwintered animals between the two areas (assessed by the distribution of eye lens masses from autopsy samples). Although the population differences in reproductive traits were to some degree also present among the overwintered animals in the laboratory, we found no difference in reproductive traits in the laboratory‐born generations. There was a strongly declining seasonal trend in probability of sexual maturation both in the field and in the laboratory under ambient light conditions. However, in the field there were large population differences in the steepness of the seasonal decline that were not seen under the standardised laboratory conditions. We conclude that seasonal decline in maturation rates is governed by change in photoperiod, but that the population level variation in the shape of the decline is caused by a direct response to the environment and not due to variation in any intrinsic state of the individuals reflecting the environment experienced by the previous generation(s).

Reproductive plasticity in the reef coral Echinopora lamellosa

The reproductive timing and mature egg size of the reef coral Echinopora lamellosa were different between the northern Taiwan and southern Taiwan populations. A reciprocal transplant experiment was conducted to study the influences of environment on the observed differences in reproductive traits between the 2 populations. The reproductive timing of the transplanted colonies in southern Taiwan and mature egg size of the transplanted colonies in both northern and southern Taiwan changed, compared to those of the original populations. This suggests that these reproductive traits are plastic and environmental factors may play an important role in regulating them. Furthermore, the growth of early stage oocytes was faster and the spawning began 2 mo earlier in the transplanted southern Taiwan colonies than those of the original populations in northern Taiwan. This suggests that the timing of reproductive activity of the transplanted E. lamellosa in southern Taiwan may be accelerated by the warmer seawater temperature.

Reproductive biology of island and mainland populations of Primula mistassinica (Primulaceae) on Lake Huron shorelines

To investigate the influence of insularity on plant reproductive biology at a local geographic scale, we examined aspects of reproduction in distylous Primula mistassinica Michx. (Primulaceae) on Lake Huron shorelines of the Bruce Peninsula and adjacent Tobermory Islands in Ontario, Canada. A total of 7 mainland and 13 nearshore island populations were compared. Controlled pollinations demonstrated that P. mistassinica possesses a dimorphic incompatibility system with intermorph crosses setting significantly more seeds than self or intramorph crosses. Floral morphology, population style-morph ratios, and seed fertility were compared in mainland and nearshore island populations to determine whether there was evidence for differences in reproductive traits between these areas. Style-morph ratios did not differ significantly from equilibrium expectations, and there were no consistent differences between island and mainland populations in floral morphology or fertility. Rather, the generalized pollination system of P. mistassinica and extensive historical opportunities for colonization appear to have mitigated insular effects so that proximate ecological factors are more relevant to the current reproductive biology of populations.Key words: distyly, insularity, pollination, reproductive biology.

Evidence of environmental effects on reproductive characteristics of Nile tilapia ( Oreochromis niloticus) populations from man-made lakes of Ivory Coast

Large differences in reproductive traits were observed between populations of Oreochromis niloticus sampled in 9 manmade lakes of Ivory Coast. In order to assess whether these variations in reproductive characteristics resulted from short term adaptation or from a longer evolutionary process, living specimens were caught in the two most differentiated populations in term of life history traits, and placed in a common environment in culture conditions. Genetic analysis of fish from these two populations were performed using four microsatellite markers and revealed that both descended originally from the same strain (Bouaké station) which was constituted from broodfish initially caught in the Nile and Volta basins. Fish from the two populations were subjected to a common environment (pond and aquariums) for five months. Then, their reproductive characteristics were analysed and no significant differences were found in fecundity, egg size and spawning frequency. These results indicate that reproductive differences between the two populations, originally observed in the two reservoirs, mostly reflect the phenotypic plasticity of the species in facing different environmental conditions.

Effects of Light Intensity on the Size Structure and Establishment of Diploids and Triploids of Disporum sessile

Abstract The effects of light intensity on population growth rates (λ) of diploid and triploid experimental populations of Disporum sessile were examined by growth experiments varying light intensity and by using a projection matrix model. λ of the diploid population was shown to have greater dependence on light intensity. This parameter under good light conditions was higher than that of the triploid population, but less than that under conditions of shade. This was due to the differences in reproductive traits of both populations. Diploids produce many small daughter plantlets and seedlings, and triploids produce a few daughter plantlets. The difference in λ between the two populations should contribute to enlargement of the habitat of D. sessile.

Reproductive Characteristics of Mexican-American, Mainland Puerto Rican, and Cuban-American Women

Data from the Hispanic Health and Nutrition Examination Survey were used to investigate reproductive characteristics of Hispanic females aged 15 to 45 years. Mexican-American and Puerto Rican women reported approximately 1.9 and 1.7 live births each, respectively, whereas Cuban-American women reported 1.1. Mexican-American women were more likely to be using oral contraceptives and were more likely to have had a hysterectomy or an oophorectomy than were Cubans and Puerto Ricans. The largest percentage of tubal ligations were found among Puerto Rican women. Mexican women who had been pregnant in the previous 12 months were more likely than their Puerto Rican and Cuban-American counterparts to be breastfeeding. Further research is needed to investigate the decision processes and/or cultural variations that may be responsible for these differences in reproductive traits across national origin groups.

Microhabitat and Reproductive Traits in Populations of the Frog, Batrachyla taeniata

A comparative study of reproductive processes and habitats of northern and southern pop- ulations of Batrachyla taeniata was carried out in Chile. Differences in reproductive traits are related to climatic variability, particularly amount of rainfall and water availability. The most important difference is in the reproductive mode, namely that clutch and egg sizes are modified without changes in size of females. Batrachyla taeniata (Girard, 1854) occurs between 32?50'S to 45?25'S in Chile. In this wide range there are populations living in the cold rain forest of southern Chile (36050'S to 45?25'S) and also in the dry warm