Do highly ornamented and less parasitized males have high quality sperm? – an experimental test for parasite-induced reproductive trade-offs in European minnow (Phoxinus phoxinus)

Parasites take their resources from hosts and thus directly reduce available resources for hosts’ own body functions, such as growth and reproduction. Furthermore, parasite infections cause significant indirect costs to their hosts in terms of increased investments on immune defense. In this study, we investigated the impact of parasite infection on the sperm quality and expression of secondary sexual ornamentation (saturation of the red abdominal colouration and number of breeding tubercles) in the Eurasian minnow (Phoxinus phoxinus). We exposed minnows to a high and low dose of common nonspecific fish ectoparasite, the glochidia larvae of duck mussel (Anodonta anatina) and tested whether parasite infection leads to trade‐off in sperm quality and/or ornamental expression. We found that glochidia infection reduces the curvature of the sperm swimming trajectory, number of breeding tubercles, and possibly male competitive ability, but does not affect expression of male color ornamentation. Furthermore, glochidia infection was found to reduce sperm motility, but only when all the noninfected individuals were excluded from the model. Supporting one of the predictions by phenotype‐linked fertility hypothesis both in high‐infection and low‐infection group male breeding colouration was positively associated with sperm quality. Our results suggest that although glochidia infection may have negative impact on male reproductive success, parasite‐induced costs may not create strong trade‐off between breeding colouration and sperm quality or that such trade‐off become detectable only in resource‐limited conditions.     

Immature performance linked with exaggeration of a sexually selected trait in an armed beetle

Exaggerated traits can be costly and are often trade-off against other characters, such as life-history traits. Thus, the evolution of an exaggerated trait is predicted to affect male life-history strategies. However, there has been very little experimental evidence of the impact of the evolution of sexually selected traits on life-history traits. This study investigated whether increased investment in exaggerated traits can generate evolutionary changes in the life-history strategy for armed males. Male flour beetles, Gnatocerus cornutus, have enlarged mandibles that are used in male-male competition, but females lack this character exaggeration completely. We subjected these weapons to 11 generations of bidirectional selection and found a correlated response in pupal survival but not in larval survival or adult longevity in the male. That is, selecting for male mandibles negatively impacted survival during the production of mandibles. There is no correlated response in the life-history traits of the female.     

半夏的繁殖生物学研究

对“泰半夏”（Ｐｉｎｅｌｌｉａｔｅｒｎａｔａ（Ｔｈｕｎｂ．）Ｂｒｅｉｔ．）的块茎和珠芽栽培观察结果表明：（１）不同繁殖体的叶形和珠芽所发生的变化与实验用的播种材料有关,珠芽发生频率与叶形变化呈正相关;（２）半夏倒苗既是对不利环境条件的一种适应,也是一种有效的无性繁殖方式;（３）半夏有性繁殖是属于同株异花传粉类型,但与无性繁殖相比,有性繁殖在种质繁衍上仅起着次要作用。     

Sexual and asexual reproduction in geographically separated populations of the fissiparous asteroid Coscinasterias calamaria (Gray)

Sexual reproduction and asexual reproduction by fission were studied in four populations of Coscinasterias calamaria (Gray), two in Otago Harbour in the South Island of New Zealand and two in the North Island near Auckland. The annual reproductive cycle in both islands of New Zealand is clearly defined with a spawning season between November and January. In both sites the pyloric caeca index was approximately inverse to the gonad index cycle as found in other forcipulate asteroids. There are substantial differences in the sex ratios of mature starfish at each site studied, with 1:1 ratios in two populations, one population heavily biased towards females and the fourth consisting almost entirely of males. Morphometric variation in arm number due to splitting was studied and the frequency of splitting varied considerably between the four populations. Generally speaking sublittoral C. calamaria divide less frequently than intertidal starfish and populations in which food is less abundant or of poorer quality are more fissiparous and put less energy into sexual reproduction, than populations with plentiful readily available food in the form of mussels. The significance of the different reproductive patterns in C. calamaria is discussed.     

Geographic parthenogenesis and the common tea‐tree stick insect of New Zealand

Worldwide, parthenogenetic reproduction has evolved many times in the stick insects (Phasmatidae). Many parthenogenetic stick insects show the distribution pattern known as geographic parthenogenesis, in that they occupy habitats that are at higher altitude or latitude compared with their sexual relatives. Although it is often assumed that, in the short term, parthenogenetic populations will have a reproductive advantage over sexual populations; this is not necessarily the case. We present data on the distribution and evolutionary relationships of sexual and asexual populations of the New Zealand stick insect, Clitarchus hookeri. Males are common in the northern half of the species’ range but rare or absent elsewhere, and we found that most C. hookeri from putative‐parthenogenetic populations share a common ancestor. Female stick insects from bisexual populations of Clitarchus hookeri are capable of parthenogenetic reproduction, but those insects from putative‐parthenogenetic populations produced few offspring via sexual reproduction when males were available. We found similar fertility (hatching success) in mated and virgin females. Mated females produce equal numbers of male and female offspring, with most hatching about 9–16 weeks after laying. In contrast, most eggs from unmated females took longer to hatch (21–23 weeks), and most offspring were female. It appears that all C. hookeri females are capable of parthenogenetic reproduction, and thus could benefit from the numerical advantage this yields. Nevertheless, our phylogeographic evidence shows that the majority of all‐female populations over a wide geographic area originate from a single loss of sexual reproduction.     

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.     

Loss of complementation and the logic of two-step meiosis

Meiosis is usually a two-step process: two divisions preceded by a duplication. One-step meiosis, a single division without prior replication, is a more logical way to produce haploid gametes; moreover, one-step meiosis leads to higher variabilty in the progeny than two-step meiosis. Yet one-step meiosis is very rare in nature, and may not even exist at all. I suggest that this is because one-step meiosis, in contrast to two-step meiosis, can be easily invaded and replaced by asexual reproduction. I discuss why other existing peculiar forms of division leading to the production of haploid gametes, but not one-step meiosis, have the same effect as two-step meiosis.     

Embryo production in a parthenogenetic snail (Potamopyrgus antipodarum) is negatively affected by the presence of other parthenogenetic females

Abstract. Stimuli associated with copulatory behavior are often needed to maximize reproductive output in internally fertilized sexual taxa. Although non-pseudogamous parthenogenetic females have no need for sperm, parthenogens descended from sexual ancestors may still require copulatory stimuli to reach their full reproductive potential. Retention of physiological dependence on copulation in parthenogens could facilitate the maintenance of sexual reproduction in species where sexual and parthenogenetic individuals coexist if parthenogens do not receive enough copulatory stimuli to achieve maximal daughter production. A laboratory experiment was conducted to determine whether embryo production in parthenogenetic female snails ( Potamopyrgus antipodarum ) is dependent on male presence. Rather than male presence, this experiment showed that embryo production is affected by the number of coexisting parthenogens. Specifically, parthenogens housed with fewer other parthenogens produced significantly more embryos than parthenogens housed with a greater number of other parthenogens, regardless of male presence and total population size. This result indicates that copulatory dependence is not likely to contribute to the maintenance of sex in P. antipodarum . Instead, it demonstrates that females of P. antipodarum negatively affect each other's reproduction, and suggests that females of P. antipodarum may exert a larger competitive influence than males of P. antipodarum . Moreover, this finding raises the possibility that highly parthenogenetic and consequently female-dense populations of P. antipodarum may experience decreased reproductive output when population size is large and resources are limiting.     

不同生境中克隆植物的繁殖倾向

对克隆植物在林下、草原、荒漠、冻原、农田和水域等6种不同类型生境中的繁殖对策及其生态适应意义进行了归纳和总结。对克隆植物有性繁殖与无性繁殖之间的权衡关系及相对重要性随水分、光照和温度的变化规律进行了阐述。分析表明,在环境条件严酷地区,克隆植物的无性繁殖在种群更新中的相对重要性有所增加。对两种繁殖方式的生态功能特性进行比较,综述了有关二者权衡关系的研究成果及影响二者权衡关系的部分因素。从研究手段上对克隆植物繁殖对策的研究进行了思考与展望。     

Spatial and temporal patterns of parthenogenesis and parasitism in the freshwater snail Melanoides tuberculata

The Red Queen hypothesis predicts that sex should be more common in populations heavily infested with parasites, than in those without. This hypothesis was investigated in the aquatic snail Melanoides tuberculata, in which both sexual and parthenogenetic individuals exist in natural populations, and some populations are heavily infested by trematodes. The presence of fertile males and the higher genetic diversity of bisexual populations are indicative of sexual reproduction. We compared sites in 1990, 1999, and 2001, and we looked for a positive correlation between male and parasite frequencies. Male frequency was not correlated with the frequency of individuals infected by trematodes. This lack of correlation was reconfirmed in a retrospective power analysis. In a period of 9 years, male frequencies decreased but infection levels increased. These results do not support the Red Queen hypothesis. In samples with high male frequency the number of embryos was low, perhaps indicating that males may have a negative effect on embryo numbers. This effect of males on fitness could perhaps suggest that the cost of sex is fewer embryos. The reduction in embryo numbers may also represent a trade-off between mating and egg production costs.