Rarity and persistence

Rarity is a population characteristic that is usually associated with a high risk of extinction. We argue here, however, that chronically rare species (those with low population densities over many generations across their entire ranges) may have individual‐level traits that make populations more resistant to extinction. The major obstacle to persistence at low density is successful fertilisation (union between egg and sperm), and chronically rare species are more likely to survive when (1) fertilisation occurs inside or close to an adult, (2) mate choice involves long‐distance signals, (3) adults or their surrogate gamete dispersers are highly mobile, or (4) the two sexes are combined in a single individual. In contrast, external fertilisation and wind‐ or water‐driven passive dispersal of gametes, or sluggish or sedentary adult life habits in the absence of gamete vectors, appear to be incompatible with sustained rarity. We suggest that the documented increase in frequency of these traits among marine genera over geological time could explain observed secular decreases in rates of background extinction. Unanswered questions remain about how common chronic rarity actually is, which traits are consistently associated with chronic rarity, and how chronically rare species are distributed among taxa, and among the world's ecosystems and regions.     

Differences in pigmentation between life cycle stages in Scrippsiella lachrymosa (dinophyceae)

Various life cycle stages of cyst‐producing dinoflagellates often appear differently colored under the microscope; gametes appear paler while zygotes are darker in comparison to vegetative cells. To compare physiological and photochemical competency, the pigment composition of discrete life cycle stages was determined for the common resting cyst‐producing dinoflagellate Scrippsiella lachrymosa. Vegetative cells had the highest cellular pigment content (25.2 ± 0.5 pg · cell^?1), whereas gamete pigment content was 22% lower. The pigment content of zygotes was 82% lower than vegetative cells, even though they appeared darker under the microscope. Zygotes of S. lachrymosa contained significantly higher cellular concentrations of β‐carotene (0.65 ± 0.15 pg · cell^?1) than all other life stages. Photoprotective pigments and the de‐epoxidation ratio of xanthophylls‐cycle pigments in S. lachrymosa were significantly elevated in zygotes and cysts compared to other stages. This suggests a role for accessory pigments in combating intracellular oxidative stress during sexual reproduction or encystment. Resting cysts contained some pigments even though chloroplasts were not visible, suggesting that the brightly colored accumulation body contained photosynthetic pigments. The differences in pigmentation between life stages have implications for interpretation of pigment data from field samples when sampled during dinoflagellate blooms.     

Apparent Involvement of a β1 Type Integrin in Coral Fertilization

Integrins are involved in a wide variety of cell adhesion processes, and have roles in gamete binding and fusion in mammals. Integrins have been also discovered in the scleractinian coral Acropora millepora (Cnidaria: Anthozoa). As a first step toward understanding the molecular basis of fertilization in corals, we examined the effect of polyclonal antisera raised against recombinant coral integrins on gamete interactions in A. millepora. Antiserum raised against integrin βcn1 dramatically decreased the binding of Acropora sperm to eggs and significantly decreased fertilization rates relative to preimmune serum and seawater controls. However, the antiserum against AmIntegrin α1 did not affect significantly either sperm–egg binding or fertilization. One possible explanation for this is that AmIntegrin α1 may preferentially mediate interactions with RGD-containing ligands, whereas mammalian α6 integrin (which is most directly implicated in gamete interactions) preferentially interacts with laminin-related ligands. Our results suggest that β1 type integrins are involved in the fertilization process in Acropora and that some functions of these molecules may have been conserved between corals and mammals. A. Iguchi and L. M. Márquez contributed equally to this work.     

The contribution of post-copulatory mechanisms to incipient ecological speciation in sticklebacks

Ecology can play a major role in species diversification. As individuals are adapting to contrasting habitats, reproductive barriers may evolve at multiple levels. While pre-mating barriers have been extensively studied, the evolution of post-mating reproductive isolation during early stages of ecological speciation remains poorly understood. In diverging three-spined stickleback ecotypes from two lakes and two rivers, we observed differences in sperm traits between lake and river males. Interestingly, these differences did not translate into ecotype-specific gamete precedence for sympatric males in competitive in vitro fertilization experiments, potentially owing to antagonistic compensatory effects. However, we observed indirect evidence for impeded development of inter-ecotype zygotes, possibly suggesting an early stage of genetic incompatibility between ecotypes. Our results show that pre-zygotic post-copulatory mechanisms play a minor role during this first stage of ecotype divergence, but suggest that genetic incompatibilities may arise at early stages of ecological speciation.     

Immunochemical localization of epididymal protein DE on rat spermatozoa: Its fate after induced acrosome reaction

The localization of rat epididymal protein DE on cauda epididymis spermatozoa was studied with a specific antibody and the peroxidase antiperoxidase (PAP) immunocyto-chemical reaction. At the light microscopic level, all spermatozoa appeared to be labeled over the dorsal portion of the head, whereas tails were negative. This observation was confirmed using scanning electron microscopy. A large number of particles were seen on the external surface of the plasma membrane covering the acrosomal region and a smaller number on the postacrosomal portion. Flagella appeared free of particles. Sperm suspensions were incubated in conditions that induce capacitation and the acrosome reaction, and, in this instance, the permanence of protein DE on the vesicles and the postacrosomal region of the membrane were observed. The localization of this epididymal protein on the sperm surface is compatible with a role in the gamete interaction process.     

Characteristics of sperm of captive seabass in relation to its fertilization potential

Seabass Dicentrarchus labrax sperm concentration was high (up to 60 × 10⁹ spz ml⁻¹) but decreased significantly at the end of the reproductive season (mid-March) in monthly sampled fish. The spermiation period may be shortened by frequent stripping. Sperm can be prediluted up to 1: 128 in non-activating medium without loss of initial motility and motility duration. Immediately after activation by transfer to sea water, all the spermatozoa were motile for 10 s and then the number of motile cells decreased progressively but sharply to zero, so that the duration of sperm motility was very short (40 s). As a consequence, the fertility of seabass sperm decreased exponentially after 10 s following sperm activation and was zero by 1 min. The sperm requirements for optimal fertilization were c . 66 000 spermatozoa per egg. Scalingup of the experimental insemination procedure yielded better fertilization rates while conserving the individual differences due to the breeder pairs.     

Cloning, sequence, and function analyses of giant panda (Ailuropoda melanoleuca) CD9 gene

CD9 is a member of the tetraspanin family proteins and has recently been shown to be essential for sperm-oocyte fusion in mice. The giant panda (Ailuropoda melanoleuca) CD9 (gpCD9) cDNA was amplified for the first time by RT-PCR from ovary total RNA and cloned, sequenced and analyzed. The result revealed that the open reading frame (ORF) of gpCD9 was 681 bp, which has the same length as that of mouse. Sequence analysis and structure prediction displayed that the amino acid sequence of gpCD9 is over 80% identity to those of mammals with the conserved structures, including the four transmembrane domains (TM) and certain characteristic residues. The results of sperm-egg fusion experiments demonstrated that giant panda CD9 large extracellular loop (LEL) significantly inhibited (P < 0.05) the mouse gamete fusion when the recombinant protein was added. However, when three amino acid residues TVT (173-175) of the gpCD9 were mutated to AAA, the large extracellular loop (LELM) of mutated protein was rarely inhibiting the gamete fusion of mice. Our results may be useful in improving an insight into understanding the potential mechanism of gamete fusion and genetic characteristics of giant panda.     

河流型水牛与沼泽型水牛杂交后代(2n=49) 染色体遗传与繁殖力的研究

通过2n=50和2n=49两种核型三品种杂交水牛繁殖记录分析和其中2n=49三品种杂交水牛联会复合体及其精子染色体研究,结果表明,后者虽然公母都是可育的,由于它产生两种正常配子（n=24,n=25）和两种异常配子（n=24+1,n=25-1）,自群繁殖导致其子代染色体多态性（2n=50,2n=49和2n=48）;其异常配子,与正常配子结合,则产生非整倍性,致其繁殖力降低,表现为情期配种受胎率降低12.3%;年受胎率降低6.4%;产仔间隔长97.6天;终生（11岁）产仔数减少1.33～1.54头。 Abstract:After analysis of reproduction records of two types of karyotypes (2n=50 & 2n=49) of triple crossbreed buffaloes (TCB) and studies of synaptinemal complex and sperm chromosome of 2n=49 TCB,the results showed that 2 sorts of normal gametes (n=24 and n=25) and 2 sorts of abnormal gametes (n=24+1 and n=25-1) were produced in 2n=49 TCB.Thus,both male and female of 2n=49 TCB are reproducible,and chromosomal polymorphyism (2n=50,2n=49 & 2n=48) occurred in the progenies after intermating.But its fertility decreased because of aneuploidy combined between normal and abnormal gametes.Compared with 2n=50 TCB,the conception rates for individual inseminations and for whole year reduced 12.3% and 6.4%,calving interval were prolonged by 97.6 days,and calf numbers in its lifetime (up to 11-year old) were lower by approximate 1.5 calves,respectively.     

Sperm trading and sex roles in the hermaphroditic opisthobranch sea slug Navanax inermis : eager females or opportunistic males?

The sea slug Navanax inermis (Gastropoda, Opisthobranchia) is a well‐known example of a simultaneous hermaphrodite in which mating partners trade sperm. According to previous work by others, sperm trading follows from a general preference for the female role when the expected variance in reproductive success in the male role is higher and the risk of failure therefore larger. However, this view contradicts theoretical and empirical studies of other systems, which predict a general preference for the male role; sperm trading is assumed to follow from the fact that individuals benefit from sperm receipt as a nutritional compensation for sperm investment. In this study, we investigate the behaviour of N. inermis in more detail. In addition to observations of regular pairs, we also paired individuals with a partner that had been isolated for 33 days in order to induce changes in sex‐role preference in the non‐isolated partner. We also collected all clutches produced throughout the study to check for signs of infertility as a consequence of allosperm depletion. Fertility of field‐collected and isolated individuals suggested that sperm depletion occurs under natural conditions and may be caused by a lack of partners. Although this argues in favour of female preference, low mating rates both reduce variance in male reproductive success and remove the intent to use sperm for nutritional purposes, thus eliminating the conditions under which both hypotheses are intended to operate. The observational data indicate that animals are eager to mate as males, particularly at the beginning of a mating session. Intromissions lasted longer when a simultaneous intromission was received from the partner. Increases in intromission were recorded in non‐isolated individuals with partners which were previously isolated and therefore more attractive as females. This response would not have been expected were the female role the preferred one. A summary of the arguments concerning preference for either gender suggests some preference for the male role, but indicates that sexual preferences may actually change or become neutral within an individual, even in the course of a mating session. Overall, our results clearly confirm previously published observations of sperm trading in N. inermis . © 2003 The Linnean Society of London. Biological Journal of the Linnean Society, 2003, 78 , 105?116.