Reproductive behavior in horseshoe crabs:Does density matter?

While the four species of horseshoe crabs share many common reproductive traits with respect to their reproductive systems,they do differ with respect to their mating behavior (monogamy vs.polygynandry).Past research has attributed these differences to a number of factors including:spawning densities,operational sex ratios (OSR's),male condition (or age),environmental and/or genetic factors,or a combination thereof.Mating behaviors in the three Asian horseshoe crab species (Tachypleus gigas,T.tridentatus,an...     

Does the temporal mismatch hypothesis match in boreal populations?

The temporal mismatch hypothesis suggests that fitness is related to the degree of temporal synchrony between the energetic needs of the offspring and their food supply. The hypothesis has been a basis in studying the influence of climate warming on nature. This study enhances the knowledge on prevalence of temporal mismatches and their consequences in boreal populations, and questions the role of the temporal mismatch hypothesis as the principal explanation for the evolution of timing of breeding. To test this, we examined if synchrony with caterpillar prey or timing of breeding per se better explains reproductive output in North European parid populations. We compared responses of temperate-origin species, the great tit (Parus major) and the blue tit (Cyanistes caeruleus), and a boreal species, the willow tit (Poecile montanus). We found that phenologies of caterpillars and great tits, but not of blue tits, have advanced during the past decades. Phenologies correlated with spring temperatures that may function as cues about the timing of the food peak for great and blue tits. The breeding of great and blue tits and their caterpillar food remained synchronous. Synchrony explained breeding success better than timing of breeding alone. However, the synchrony effect arose only in certain conditions, such as with high caterpillar abundances or high breeding densities. Breeding before good synchrony seems advantageous at high latitudes, especially in the willow tit. Thus, the temporal mismatch hypothesis appears insufficient in explaining the evolution of timing of breeding.     

Does the Bicoid gradient matter?

The generation and interpretation of positional information are key processes in developmental systems. In this issue, Chen et?al. report discoveries made in the Drosophila embryo that give new insights into how positional information can be produced by patterning gradients.     

Nereis succinea nuptial behavior: Does size matter?

Summary

Although Darwin noted that size may affect sexual selection, the effect of size on reproduction is controversial. Mature Nereis succinea, a polychaete that mates in pheromone-mediated twilight nuptial swarms, varies greatly in size, ranging more than 10-fold in body weight from 30 mg to >300 mg. Swim speed of swarming male worms increases with worm size, with the fastest males swimming more than twice the speed of the slowest. The female-produced spawning pheromone, nereithione, stimulates both swimming speed and spawning in males at concentrations of 10^?6 M and above, and lower concentrations cause significant activation of swimming. Individual worms can be stimulated to release sperm up to 40 or more times in a single experimental session. Larger worms release cumulatively more sperm than smaller ones, resulting in significant loss of body mass from repetitive spawning activated by nereithione. Size may enhance mating success of male N. succinea due to encountering more females as a result of faster swimming speed and due to the higher sperm density and number of spawning responses of large animals.     

Does individual variation in stress responses and agonistic behavior reflect divergent stress coping strategies in juvenile rainbow trout?

Individual rainbow trout were transferred to visual isolation in experimental aquaria. As a measure of the speed of acclimation, individual food intake was quantified during the first 6 d following transfer. Following acclimation, aggression was quantified by subjecting the fish to three resident-intruder tests, with 30 d of recovery between the tests. Moreover, between the resident-intruder tests (i.e., two times) the fish were exposed to an unfamiliar environment and their cortisol response was measured. The results of this study show that individuals of juvenile rainbow trout differ distinctly in their response to changes in their environment, and that this diversity in behavior is reflected by consistent behavioral traits displayed by individual fish. These traits have proven to be consistent not only over time but also across situations, revealing two distinct behavioral profiles, in the same manner as shown in studies on proactive and reactive mammals. Our results also show that the reactivity of the hypothalamic-pituitary-interrenal (HPI) axis, when exposed to a stressor, is a consistent physiological trait in juvenile rainbow trout. We found that difference in HPI axis reactivity is linked to the different behavioral profiles. However, HPI axis reactivity could not be linked directly to the singular behavioral traits measured. In other words, we did not find that the consistent behavioral traits shown by the fish were associated with a difference in HPI axis reactivity in the same manner as the reactivity of the hypothalamic-pituitary-adrenocortical axis does in mammals. Taken together, our results show that stress coping strategies akin to what has been described as reactive and proactive stress coping in mammals appear to exist in juvenile rainbow trout.     

Omnivory and stability in freshwater habitats: Does theory match reality?

相似文献   

Do random fluctuations in the intervals between feeding affect growth rate in juvenile three-spined sticklebacks?

This study measured the effects of regular and irregular intervals between feeds on the growth performance of juvenile Gasterosteus aculeatus . The experimental period was 21 days at 14) C and photoperiod of 10L: 14D. The fish were housed individually. The control fish received a constant ration every day. Fish on a constant interval were fed on days 1, 5, 9, 13, 17 and 21. Fish on a random regime were fed with the same average interval between feedings, but the interval varied randomly between 1 and 5 days. The rations were calculated so that over the 21-day period, all fish were supplied with the same total quantity of food. The two ration levels were: 2% (maintenance ration) and 6% of the initial body weight per day. At a given ration, the feeding interval had no significant effect on specific growth rate, RNA/DNA ratio and lipid contents. The percentage dry matter was slightly, but significantly lower in treatment groups than in the control group. Groups receiving a mean 2% ratio consumed all the food supplied. At a mean ration of 6%, the control group ate 100%, the regular interval group 95·4% and the irregular interval 98·3% of the total food supplied. For the temporal patterns of feeding used, the fish were able to adjust their food intake, when food become available, to compensate for short periods of food deprivation and maintain their growth performance except for a decrease in dry matter content.     

Does biology underlie the oldest profession? Prostitution and sex disparities in john behavior

This study considers a biosocial explanation of why johns, the purchasers of commercial sex exchanges, are almost exclusively male. Trivers's theory of parental investment and sexual selection predicts that differential parental investment by biological sex will lead to divergent sex-based reproductive instincts. The sex bearing the larger parental investment will tend to be choosier whereas the sex bearing the lesser investment will tend to be relatively indiscriminate and competitive for access to sexual resources. We hypothesized that men are more likely than women to offer objects of value in exchange for access to sexual resources. Using self-reports of sex-purchasing from Add Health data (N = 14,544), we found that maleness was a robust predictor of john behavior even after controlling for well-known criminogenic risk factors.     

Does colonization asymmetry matter in metapopulations?

Despite the considerable evidence showing that dispersal between habitat patches is often asymmetric, most of the metapopulation models assume symmetric dispersal. In this paper, we develop a Monte Carlo simulation model to quantify the effect of asymmetric dispersal on metapopulation persistence. Our results suggest that metapopulation extinctions are more likely when dispersal is asymmetric. Metapopulation viability in systems with symmetric dispersal mirrors results from a mean field approximation, where the system persists if the expected per patch colonization probability exceeds the expected per patch local extinction rate. For asymmetric cases, the mean field approximation underestimates the number of patches necessary for maintaining population persistence. If we use a model assuming symmetric dispersal when dispersal is actually asymmetric, the estimation of metapopulation persistence is wrong in more than 50% of the cases. Metapopulation viability depends on patch connectivity in symmetric systems, whereas in the asymmetric case the number of patches is more important. These results have important implications for managing spatially structured populations, when asymmetric dispersal may occur. Future metapopulation models should account for asymmetric dispersal, while empirical work is needed to quantify the patterns and the consequences of asymmetric dispersal in natural metapopulations.     

Does the order of second-line treatment in rheumatoid arthritis matter?

In a prospective study 88 patients, with rheumatoid arthritis who had stopped taking gold, penicillamine, or levamisole were randomly allocated to one of the alternative drugs and followed up for a minimum of one year. Concurrent studies of the effects of gold, penicillamine, and levamisole prescribed in 123 patients as the first second-line drug were used for comparison. No difference in toxicity or efficacy between primary and secondary use of gold or penicillamine was identified. Variation in the toxicity of levamisole could in part be accounted for by changes in the dose regimen over the four years of study. The length of the treatment-free interval between drugs did not influence subsequent development of toxicity. These results suggest that an adverse reaction to one of the three second-line drugs studied should not prejudice the selection of another.     

Quail and rain in semiarid rangelands: Does management matter?

Rainfall is a strong driver of quail populations on southwestern rangelands and can account for a large portion (~70–95%) of the variability in regional quail production and abundance. Landowners have attempted to moderate these boom-and-bust fluctuations via management; however, presently it is unknown whether management can increase or stabilize quail populations in semiarid environments or whether rainfall remains as influential at small spatial extents. Our objectives were to evaluate the efficacy of management at mitigating the effects of rainfall on northern bobwhite (Colinus virginianus) populations on semiarid rangelands and to quantify the influence of rainfall on bobwhite density at smaller spatial extents. We conducted a study to evaluate these objectives during 2014–2020 in the Rio Grande Plains (n = 11 sites; 1,100‒6,500 ha) and Rolling Plains (n = 4 sites; 1,900‒4,000 ha) of Texas, USA. We estimated bobwhite density during late autumn (Dec‒Jan) on all sites using helicopter surveys within a distance-sampling framework. We also obtained site-level seasonal rainfall (Apr‒Aug) and quantified management intensity via landowner surveys and a scoring rubric to categorize sites into 3 classes (low, medium, and high management intensity). Bobwhite populations during this study experienced a boom-bust cycle in both the Rio Grande Plains and Rolling Plains, with mean bobwhite density fluctuating considerably (0.57‒2.96 bobwhites/ha and 0.02‒2.88 bobwhites/ha, respectively). In the Rio Grande Plains, mean bobwhite density significantly increased from low to high management intensity in 2015 (1.12 ± 0.17 bobwhites/ha vs. 2.87 ± 0.39 bobwhites/ha, respectively), 2016 (1.06 ± 0.20 bobwhites/ha vs. 2.96 ± 0.36 bobwhites/ha, respectively), 2017 (0.73 ± 0.16 bobwhites/ha vs. 1.91 ± 0.32 bobwhites/ha, respectively), and 2019 (0.42 ± 0.14 bobwhites/ha vs. 1.01 ± 0.26 bobwhites/ha, respectively; P < 0.05). In addition, rainfall at the site level accounted for a low amount of the variation in bobwhite density (r² = 0.09; P < 0.01). Similarly, in the Rolling Plains, mean bobwhite density significantly increased from low to high management intensity in 2015 (1.30 ± 0.27 bobwhites/ha vs. 2.20 ± 0.29 bobwhites/ha, respectively) and 2016 (1.26 ± 0.26 bobwhites/ha vs. 2.88 ± 0.34 bobwhites/ha, respectively; P < 0.05). Rainfall at the site level also accounted for a low amount of the variation in bobwhite density (r² < 0.02; P = 0.82). Our findings suggest that management can increase bobwhite density beyond that of less-managed properties but does not completely eliminate inter-annual fluctuations in semiarid environments. In addition, rainfall appears to exert less of an influence on bobwhite density at a site level (e.g., 2,000 ha) than has been documented at a regional level (e.g., ≥8 million ha).     

Does size really matter? Weight and values in public health

The medical community has long regarded obesity and overweight as serious health risks, and popular culture reflects these concerns. A focus on body weight reduction motivates many contemporary exercise and diet practices, especially among women. Yet, there is significant evidence that those risks have been exaggerated, that weight loss regimens may be more detrimental to health than moderate obesity, and that pressure to be thin leads to disordered eating and unhealthy lifestyle choices. This paper examines the problematic manners in which some national health policies regard the problems of overweight and obesity. It contends that concepts of aesthetics, grounded in 19th-century beliefs about the body, guide clinicians to emphasize measurement of the body in health assessment at potential cost to individual wellness.     

Does the location of enrichment material affect behavior and dirtiness in growing female pigs?

The objective of this study was to investigate if female growing pigs spend similar amounts of time exploring a wooden stick as they do exploring enrichment material regardless of its proximity to the feeder. Forty-eight pigs aged 18 to 26 weeks allocated to 16 pens with three pigs per pen were studied. Fifty percent of the pens had a wooden stick beside the feeder, and the rest had a similar stick opposite to the feeder. Two observers assessed the pigs by means of scan and focal sampling. The pigs spent more time (p < .0001) exploring the wood during the first week than during the rest of the study (10.9% vs 3.6%). The pigs with the wood close to the feeder spent less (p = .0001) time resting (29.9%) and more (p < .0001) time exploring (6.3%) the wood than did pigs with the wood opposite to the feeder (32.4% and 2.5%, respectively). In conclusion, a wooden stick placed close to the feeder was associated with more exploratory behaviorcompared with a similar stick placed opposite to the feeder.     

Does size matter?

For 40 years, the debate has raged. Do mammalian cells monitor cell size when deciding whether to divide? More recent models suggest an indirect solution, but the field is far from reaching a final verdict.