176 research outputs found
Male Genital Morphology and Its Influence on Female Mating Preferences and Paternity Success in Guppies
In internally fertilizing species male genitalia often show a higher degree of elaboration than required for simply transferring sperm to females. Among the hypotheses proposed to explain such diversity, sexual selection has received the most empirical support, with studies revealing that genital morphology can be targeted by both pre-and postcopulatory sexual selection. Until now, most studies have focused on these two episodes of selection independently. Here, we take an alternative approach by considering both components simultaneously in the livebearing fish, Poecilia reticulata. We allowed females to mate successively (and cooperatively) with two males and determined whether male genital length influenced the female's propensity to mate with a male (precopulatory selection, via female choice) and whether male genital size and shape predicted the relative paternity share of subsequent broods (postcopulatory selection, via sperm competition/cryptic female choice). We found no evidence that either episode of sexual selection targets male genital size or shape. These findings, in conjunction with our recent work exposing a role of genital morphology in mediating unsolicited (forced) matings in guppies, further supports our prior speculation that sexual conflict may be an important broker of genital evolution in this species
Numerical Investigation on the Thermo-Mechanical Behavior of HTS Tapes and Experimental Testing on Their Critical Current
This work extends to second generation Rare-Earth Barium-Copper-Oxide ((Re)BCO) tapes an experimental proce- dure previously developed to analyze the impact of double bending at room temperature on the performance of Bismuth-Strontium- Calcium-Copper-Oxide (BSCCO) tapes. The modified procedure is applied to measure the critical current of a commercial (Re)BCO tape subjected to bending around a cylindrical mandrel first on one side, then on the other side, followed by the cooldown to cryogenic temperature. In the bending phase, mandrels of decreasing diame- ter are used to identify the minimum curvature leading to a signif- icant reduction of the tape critical current. Furthermore, a novel finite element model is developed to complement the experimental results. The model simulates the double bending at room tempera- ture, the following straightening of the sample, and its cooldown to cryogenic conditions. The coupled thermo-mechanical numerical model together with the temperature-dependent mechanical prop- erties allow investigating the combination of thermal contraction effects and bending loads in the whole domain of the problem. The experimental and numerical results obtained help to give a better insight in the distribution of the strain and stress components inside the (Re)BCO tape and to evaluate their impact on the conductor electrical performance in relevant operating condition
Possible glimpses into early speciation: the effect of ovarian fluid on sperm velocity accords with post-copulatory isolation between two guppy populations.
Identifying mechanisms of reproductive isolation is key to understanding speciation. Among the putative mechanisms underlying reproductive isolation, sperm-female interactions (postmating-prezygotic barriers) are arguably the hardest to identify, not least because these are likely to operate at the cellular or molecular level. Yet sperm-female interactions offer great potential to prevent the transfer of genetic information between different populations at the initial stages of speciation. Here we provide a preliminary test for the presence of a putative postmating-prezygotic barrier operating between three populations of Trinidadian guppies (Poecilia reticulata), an internally fertilizing fish that inhabits streams with different levels of connectivity across Trinidad. We experimentally evaluate the effect of female ovarian fluid on sperm velocity (a predictor of competitive fertilization success) according to whether males and females were from the same (native) or different (foreign) populations. Our results reveal the potential for ovarian fluid to act as a postmating-prezygotic barrier between two populations from different drainages, but also that the strength of this barrier is different among populations. This result may explain the previous finding that, in some populations, sperm from native males have precedence over foreign sperm, which could eventually lead to reproductive isolation between these populations. This article is protected by copyright. All rights reserved
Considerations on the use of video playbacks as visual stimuli: The Lisbon workshop consensus
This paper is the consensus of a workshop that
critically evaluated the utility and problems of video
playbacks as stimuli in studies of visual behavior. We
suggest that video playback is probably suitable for
studying motion, shape, texture, size, and brightness.
Studying color is problematic because video systems are
specifically designed for humans. Any difference in color
perception must lead to a different color sensation in
most animals. Another potentially problematic limitation
of video images is that they lack depth cues derived from
stereopsis, accommodation, and motion parallax. Nonetheless,
when used appropriately, video playback allows
an unprecedented range of questions in visual communication
to be addressed. It is important to note that most
of the potential limitations of video playback are not
unique to this technique but are relevant to all studies of
visual signaling in animals
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