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175 results for “Viviparity”
A global analysis of viviparity in squamates highlights its prevalence in cold climates
<p>Aim: Viviparity has evolved more times in squamates than in any other vertebrate group. Therefore, squamates offer an excellent model system to study the patterns, drivers, and implications of reproductive mode evolution. Based on current species distributions we examined three selective forces hypothesized to drive squamate viviparity evolution: (1) cold climate, (2) variable climate, and (3) hypoxic conditions, and tested whether viviparity is associated with larger body size.</p> <p>Location: Global.</p> <p>Time period: present day.</p> <p>Taxon: Squamata.</p> <p>Methods: We compiled a dataset of 9,061 squamate species including their distributions, elevation, climate, body mass, and reproductive modes. We applied species-level and assemblage-level approaches for predicting reproductive mode, globally and within biogeographical realms. We tested the relationships of temperature, interannual and intra-annual climatic variation, elevation (as a proxy for hypoxic conditions), and body mass with reproductive mode, employing path analyses to account for correlations among the environmental predictors.</p> <p>Results: Viviparity was strongly associated with cold climates at both species and assemblage levels, despite the prevalence of viviparity in some warm climates. Viviparity was not clearly correlated with climatic variability or elevation. The probability of being viviparous was weakly positively correlated with body size.</p> <p>Conclusions: Although phylogenetic history is important, potentially explaining the occurrence of viviparous species in presently warm regions, current global squamate distribution is characterized by a higher relative abundance of viviparity in cold environments – supporting the prediction of the 'cold-climate' hypothesis. The roles of climatic variation and of hypoxia are less important and not straightforward. Elevation probably exerts various selective pressures and influences the prevalence of viviparity primarily through its effect on temperature rather than on oxygen concentration.</p>
Fig. 4 in First report of viviparity of the stoneflies Capnia khingana (Plecoptera: Capniidae) in the Low Amur River Basin
Fig. 4. Female of Capnia khingana hatched embryos: A – first instar nymph exiting of
Fig. 5 in First report of viviparity of the stoneflies Capnia khingana (Plecoptera: Capniidae) in the Low Amur River Basin
Fig. 5. Female of Capnia khingana giving birth to first instar nymph.
Fig. 3 in First report of viviparity of the stoneflies Capnia khingana (Plecoptera: Capniidae) in the Low Amur River Basin
Fig. 3. Female of Capnia khingana with developing eggs, non hatched and hatched
Fig. 2 in First report of viviparity of the stoneflies Capnia khingana (Plecoptera: Capniidae) in the Low Amur River Basin
Fig. 2. Female of Capnia khingana with developing nymphal embryos throughout
Fig. 1 in First report of viviparity of the stoneflies Capnia khingana (Plecoptera: Capniidae) in the Low Amur River Basin
Fig. 1. Female reproductive system of Capnia khingana. Abbreviations: Ov – developing
Fig. 7 in Ecophysiological responses to the effect of annual management on an endemic viviparous fish in central plateau of México
Fig. 7. Bimonthly energy expenditure during cycles of mexcalpique nictemeral in San Martin.
Fig. 1. Environmental parameters during a in Ecophysiological responses to the effect of annual management on an endemic viviparous fish in central plateau of México
Fig. 1. Environmental parameters during a hydrological cycle in San Martín Dam.
Figure 6 in State of knowledge of viviparity in Staphylinidae and the evolutionary significance of this phenomenon in Corotoca Schiødte, 1853
Figure 6. Scheme illustrating part of the life cycle of Corotoca sp. Left (A) shows hypothetical case of dispersion made by the adult, while the right (B) illustrates the hypothesis proposed in this work, of dispersion mainly by immature.
Figure 2 in State of knowledge of viviparity in Staphylinidae and the evolutionary significance of this phenomenon in Corotoca Schiødte, 1853
Figure 2. Estação Experimental São João do Cariri, located at São João do Cariri municipality, Paraiba State, northeastern of Brazil.
Figure 3 in State of knowledge of viviparity in Staphylinidae and the evolutionary significance of this phenomenon in Corotoca Schiødte, 1853
Figure 3. Corotoca phylo SchiØdte, 1853, female (= paratype of C. seeversi Fontes, 1977). (A) transversal cut of curvature of the abdomen, with two exposed eggs, each with an embryo in different stage of development in relation to another; (B) transversal cut od abdomen from segment IV, with exposed larva; (C) habitus lateral. Scales: 0.5 mm.
Fig. 7 in Nomorhamphus Rex, A New Species Of Viviparous Halfbeak (Atherinomorpha: Beloniformes: Zenarchopteridae) Endemic To Sulawesi Selatan, Indonesia
Fig. 7. Toletole River, type locality of Nomorhamphus rex. (Photography by: Suzanne M. Gray).
Pleistocene divergence in the absence of gene flow among populations of a viviparous reptile with intraspecific variation in sex determination
<p>Polymorphisms can lead to speciation if there is differential mating success among conspecifics divergent for a trait. Polymorphism for sex determining system might be particularly expected to isolate gene pools, given strong selection for the production of viable males and females and the low success of heterogametic hybrids when sex chromosomes differ (Haldane's rule). We investigated this question using a rare example of a species exhibiting polymorphism for sex determination: the viviparous snow skink <i>Carinascincus ocellatus</i>. While a coparatively high elevation population has entirely genotypic sex determination, in a lower elevation population there is an additional environmental component to sex determination. These systems also exhibit minor differences in sex-linked genotypes. Using 'Isolation with Migration' analysis of neutral loci, we estimated that these populations and their sex determining systems diverged in the absence of gene flow, across multiple periods of geographic proximity during Pleistocene glaciations. Our analysis suggests that populations of <i>C. ocellatus</i> with divergent sex determining systems are likely reproductively isolated, even though they are presently underlined by only subtle DNA differences. Given the influence of temperature on sex in one lineage, we also discuss the implications for the persistence of this polymorphism under climate change.</p>
Interpreting morphological adaptations associated with viviparity in the Tsetse fly (Glossina morsitans) by three-dimensional analysis
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Viviparity is associated with larger female size and higher sexual size dimorphism in a reproductively bimodal lizard
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Resource-dependent investment in male sexual traits in a viviparous fish
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Pleistocene divergence in the absence of gene flow among populations of a viviparous reptile with intraspecific variation in sex determination
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A global analysis of viviparity in squamates highlights its prevalence in cold climates
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Data from: Viviparity does not affect the numbers and sizes of reptile offspring
<ol> <li>Viviparity (live-bearing) has independently evolved from oviparity (egg-laying) in more than 100 lineages of squamates (lizards and snakes).</li> <li>We might expect consequent shifts in selective forces to affect per-brood reproductive investment (RI = total mass of offspring relative to maternal mass) and in the way in which that output is partitioned (number <i>versus</i> size of offspring per brood). Based on the assumption that newly-born offspring are heavier than eggs, we predicted that live-bearing must entail either increased reproductive investment or a reduction in offspring size and/or fecundity.</li> <li>However, our phylogenetically-controlled analysis of data on 1,259 squamate species revealed no significant differences in mean offspring size, clutch size or RI between oviparous and viviparous squamates.</li> <li>We attribute this paradoxical result to (1) strong selection on optimal offspring sizes, unaffected by parity mode, (2) the lack of a larval stage in amniotes, favouring large eggs even in the ancestral oviparous mode, and (3) the ability of viviparous females to decrease the mass of uterine embryos by reducing extra-embryonic water stores.</li> <li>Our analysis shows that squamate eggs (when laid) weigh about the same as the hatchlings that emerge from them (despite a many-fold increase in embryo mass during incubation). Most of the egg mass is due to components (such as water stores and the eggshell) not required for oviductal incubation. That repackaging enables live-born offspring to be accommodated within the mother's body without increasing total litter mass.</li> <li>The consequent stasis in reproductive burden during the evolutionary transition from oviparity to viviparity may have facilitated frequent shifts in parity modes.</li> </ol>
FIGURE 1 in Two new aphid species of the genus Cryptomyzus Oestlund, 1922 (Hemiptera Aphididae) from Kazakhstan, and keys to apterous and alate viviparous females
FIGURE 1. Cryptomyzus sairamugamicus sp. n.: a—body; b—third antennal segments; c—ultimate rostral segment; d—dorsal hair; e—siphunculus; f—cauda.
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