Dormancy and the influence of photoperiod and temperature on sexual maturity in Nicrophorus nepalensis (Coleoptera: Silphidae)

Abstract Carrion beetles (Nicrophorus spp.) use small vertebrate carcasses for food and reproduction. Their ecology and behaviors are highly affected by the availability of carcasses and the surrounding environmental conditions. Our results revealed that in subtropical Fushan, northern Taiwan, N. nepalensis was mainly active in spring (February to May), and could also be found in autumn (October and November); but there was no capture record in summer (June to September) and winter (December and January). A laboratory temperature tolerance study indicated that N. nepalensis adults become inactive at temperatures above 26°C, and had the highest mortality when the temperature was raised from 27°C to 28°C. Furthermore, N. nepalensis became sexually mature at 20°C, depending on the photoperiod: the longer the day, the lower the percentage of sexually mature 2‐week‐old females after emergence. In another experiment, N. nepalensis virgins were paired under three possible conditions at Fushan. At 15°C and 20°C, if carcasses were presented to the pairs within 3 days after emergence, all laid eggs in the second week after emergence. If carcasses were presented 1 week after emergence, most began to reproduce at 20°C with 12.5 h of daylight. However, at 15°C with 11 h of daylight, the carrion beetles hibernated first, and reproduced in the ninth week after emergence. At 25°C with 14 h of daylight, carrion beetles did not bury the mouse carcasses, the females did not lay eggs, and the adult lifespan was only one‐third of that at 20°C. This study revealed that both photoperiod and temperature influence the time needed to reach the sexual maturity of N. nepalensis; and also implied that the narrow temperature tolerance range and dormancy behavior of carrion beetles are highly regulated by those environmental factors.     

Size at the onset of sexual maturity in the anomuran crab, Aegla uruguayana (Aeglidae)

The size at maturity was studied in the crab Aegla uruguayana from the Areco River (31°14′ S, 59°28′ W), Argentina. Size at sexual maturity was determined according to three criteria: morphometric (change in the relative growth of reproductive characters), histological (first maturation of gonads) and functional (capability to mate and carry eggs). Regarding females, morphometric maturity occurred at a carapace length (CL) of 11.50 mm, considering abdomen width as a reproductive character. Gonad maturity of females could be observed at a minimum size ranging from 15 to 17 mm CL. The smallest ovigerous female observed in the field was 15.60 mm CL, although a relevant population incidence of ovigerous females (86.6%) has just been observed at values higher than 17 mm CL. As for males, the relative growth of the left chela length changed at a value of 15.40 mm CL, while morphological changes in sexual tube occurred between CL of 14 and 16 mm. Testicular maturation occurred at a CL ranging from 17 to 19 mm. The smallest size of males having spermatozoids in their vasa deferentia was 18.70 mm CL. The results obtained indicated that, in both sexes, functional maturity occurred after morphometric maturity and at a size similar to that of gonad maturity. Comparing sexes, females acquired sexual maturity (morphometric, gonad and functional maturity) at sizes statistically smaller than those of males.     

Extended Breeding Season in the Marbled Goby, Pomatoschistus Marmoratus (Teleostei: Gobiidae), in the Venetian Lagoon

Life cycle and reproductive biology of the marbled goby Pomatoschistus marmoratus was studied in the Venetian Lagoon. Lifespan was determined by reading otoliths. The maximum age recorded was 17 months juveniles occurred in samples from July to November. Nests were found in two different periods: from the middle of April to the middle of July and from the middle of August to the end of September. While individuals in a wide range of body size (35–62mm total length) mated during the first spawning peak during the second one only small individuals (28–32mm total length) developed during the first peak were in reproductive activity. Histological analyses showed that most of the juveniles developed during the first spawning peak delayed sexual maturation to the following year. Ripe females appeared to be multiple spawner showing an asynchronous ovary with oocytes at different stages of development. From nesting male body sizes gonadosomatic indices and histological analyses no indication of the presence of alternative male mating tactics emerged.     

REPRODUCTION SEXUÉE D'UNE ASTÉRIE FISSIPARE,SCLERASTERIAS RICHARDI (PERRIER, 1882) / SEXUAL REPRODUCTION IN A FISSIPAROUS ASTEROID,SCLERASTERIAS RICHARDI (PERRIER, 1882)

Sclerasterias richardi, a relatively deep sea asteroid (140–200 m) from the border of the Mediterranean continental shelf, is characterized by an asexual reproduction by fissiparity concomitant with a functional sexuality.

A monthly sampling of a population from Calvi (Corsica) has allowed a study of the complete sexual cycle from 354 histologically-treated specimens.

The 218 sexually defined animals (62% males, 38% females) show strict gonochorism. In males, spermatogenesis is cyclic and sexual maturity seems to be reached before that of the females. In females, the different stages of oogenesis are well marked: oogonia and parietal oocytes disappear only at maturity. Oligolecithic oocytes (120–150 μn) show a synchronous growth.

The annual reproductive cycle is well defined in both sexes with one spawning period from mid-September to mid-October.

After spawning, a resting period (from mid-October to mid-January) occurs during which unspawned oocytes are phagocytized by more or less isolated accessory cells. These phagocytic cells have never been found in male specimens.

Each month the presence of specimens without gonads or unsexable individuals is one of the characteristics of this cycle. Their high proportion during the organization stage and after spawning can be easily explained. In March they are frequent too, owing to the infestation of gonads by Ciliates.

As shown by our samples, the bottom water temperature is nearly the same during the whole year and cannot be directly involved as the dominant exogenous variable stimulating spawning.

As a consequence of fissiparity which affects the main part of the population there is a great inter- and intra-individual variability.

The reproductive potentiality is low: as a female emits approximatly 400–500 ova whose development produces planktotrophic larvae with a long pelagic life, it is clear that sexual reproduction is accessory in comparison with asexual reproduction by fission.     

青藏高原及周边高山地区的植物繁殖生态学研究进展

青藏高原及周边高山地区孕育了极为丰富的植物多样性资源, 研究该地区植物如何顺利完成繁殖过程有助于我们理解植物对典型高山环境的进化和适应机制。该文综述了青藏高原地区高山植物在资源分配、繁殖方式、花部特征演化等方面的研究进展, 包括全球气候变化对植物繁殖特征的影响, 以及一些新技术和新方法在本研究领域的应用。在高山地区限制性环境中, 随海拔升高, 繁殖分配通常表现出增大的趋势, 其中投入到雄性资源的比例上升, 但具体的资源分配模式还要取决于植株的交配系统、个体大小、生活史特征、遗传特性以及环境中的资源有效性等。面对资源和传粉的双重限制, 植物在不同繁殖方式之间存在权衡, 当传粉者稀少时, 克隆繁殖和自交有利于繁殖保障; 而有性繁殖和异交能够提高种子的质量和后代的遗传多样性, 从而在复杂多变的气候条件下有利于种群的维持。因此, 不同繁殖方式的结合以及泛化的传粉互作网络可能是应对高山限制性环境的最优选择。花部特征的演化主要受到当地传粉者的选择压力, 但是外来传粉者、植食者、盗蜜者以及非生物环境(如温度、雨水和紫外辐射等)对花部性状的影响越来越受到重视。近年来, 青藏高原因其脆弱性和对气候变化的高度敏感性而在全球气候变化研究中备受关注, 以全球变暖和氮沉降增加为显著特征的全球气候变化正在直接或间接地影响着该地区高山植物的繁殖特征。气候变化影响植物和传粉者的物候并引起物种的迁移, 最终将导致植物与传粉者的时空不匹配。植物通过改变花部特征(花展示、花冠结构、花报酬的数量和质量)来响应气候变化, 这可能会改变其传粉者的类型、数量和访花行为, 从而最终影响植物的繁殖成功。3D打印和高通量测序等新技术和新方法的应用有助于促进植物繁殖生态学研究的进一步发展。3D打印的花能够精确控制其形态构造, 可以用于研究精细的花部特征变化对于传粉者行为的影响, 在此基础上与人工饲养的传粉者结合使用, 有助于进一步研究传粉者介导的花部特征演化。随着高通量测序技术的发展, 植物繁殖生态学领域, 尤其是花部特征演化的许多重要问题的潜在机制得以深入研究。该文最后提出了目前研究中需要注意的问题以及值得深入研究的发展方向。     

Effects of starvation on growth and reproductive apparatus of two immature freshwater snails Biomphalaria pfeifferi and Biomphalaria glabrata (Gastropoda: Planorbidae)

Starvation of immature snails of Biomphalaria pfeifferi and B. glabrata results in an arrest of growth and animals remain immature. Spermatogenesis is limited to spermatogonia (B.g.) or spermatocytes 1 (B.p.). The number and the size of oocytes remain inferior to that of controls. Animals show reduced genital tracts.Once feeding is restored, growth is resumed but wet weight and shell diameter do not reach the same level as in controls. Fecundity and gametogenesis do not differ from that in controls. Genital tracts weight is proportional to body weight.     

Different Responses of Sexual and Asexual Reproduction of Arundinella hirta to Flooding

The sexual and asexual reproductive features of the graminoid species Arundinella hirta growing at riversides of the Jialing River were analyzed.It was found that the total seed mass,seed number per plant,and sexual reproductive allocation of A.hirta decreased with decreasing bank elevation,and plants growing at the lowest elevations of banks subjected to intense flooding did not show sexual reproduction.The total plant biomass and the number of ramifications per plant increased with flooding intensity,which implies that,contrary to sexual reproduction,asexual reproduction of A.hirta was enhanced by flooding.     

Population structure and reproduction of the longtail grass shrimp Urocaris longicaudata (Decapoda,Caridea, Pontoniinae) in Laguna de Términos,SW Gulf of Mexico

The purpose of this study was to describe the population structure and some reproductive traits of Urocaris longicaudata collected in Laguna de Términos, Campeche, Mexico in October and December 2009, and February and April 2010. A total of 2977 specimens were collected of which 1596 were females (including 276 ovigerous) and 1381 were males. Females were larger than males (2.03 ± 0.63 vs. 1.97 ± 0.44 mm carapace length (CL), respectively). The overall sex-ratio differed significantly from 1:1. The reproductive period was apparently continuous, with most ovigerous females recorded from December 2009 to April 2010. The estimated size at sexual maturity in females was 2.90 ± 0.64 mm CL. A significant and positive linear relationship between CL and realised fecundity was estimated. The number of embryos ranged from 33 to 320. The average volume of newly spawned embryos was 0.038 ± 0.009 mm³ and that of those near hatching was 0.062 ± 0.012 mm³, representing a 63.15% increase throughout embryogenesis. The females lost on average 27.6% of the initially produced embryos during the incubation period, which favoured the survival of the remaining embryos. This is the first report on any biological trait of U. longicaudata along the southwestern Gulf of Mexico.