Maria B. Rasotto

Colourful male guppies produce faster and more viable sperm

In guppies (Poecilia reticulata) precopulatory sexual selection (via female choice) and post‐copulatory selection (via sperm competition) both favour males with relatively high levels of carotenoid (orange) pigmentation, suggesting that colourful males produce more competitive ejaculates. Here we test whether there is a positive association between male orange pigmentation and sperm quality. Our analysis of sperm quality focused on sperm swimming speeds (using CASA: computer‐assisted sperm analysis to estimate three parameters of sperm velocity in vitro), sperm viability (proportion of live sperm per stripped ejaculate) and sperm lengths. We found that males with relatively large areas of orange pigmentation had significantly faster and more viable sperm than their less ornamented counterparts, suggesting a possible link between dietary carotenoid intake and sperm quality. By contrast, we found no relationship between sperm length (head length and total sperm length) and male phenotype. These findings, in conjunction with previous work showing that highly ornamented male guppies sire higher quality offspring, suggest that female preference for colourful males and sperm competition work in concert to favour intrinsically higher quality males.

Individual adjustment of sperm expenditure accords with sperm competition theory

Sperm competition theory predicts that males should strategically allocate their sperm reserves according to the level of sperm competition, defined as the probability that the sperm of two males compete for fertilizing a given set of ova. Substantial evidence from numerous animal taxa suggests that, at the individual level, sperm expenditure increases when the risk of sperm competition is greater. In contrast, according to the “intensity model” of sperm competition [Parker, G. A., Ball, M. A., Stockley, P. & Gage, M. J. G. (1996) Proc. R. Soc. London Ser. B 263, 1291–1297], when more than two ejaculates compete during a given mating event, sperm expenditure should decrease as the number of competing males increases. Empirical evidence supporting this prediction, however, is still lacking. Here we measured sperm expenditure in two gobiid fishes, the grass (Zosterisessor ophiocephalus) and black goby (Gobius niger), in which up to six sneakers can congregate around the nest of territorial males and release their sperm when females spawn. We show that, in accordance with theory, sneaker males of both species release fewer sperm as the number of competitors increases.

Sperm Competition and Mode of Fertilization in the Grass Goby Zosterisessor ophiocephalus (Teleostei: Gobiidae)

2 AND ABSTRACT Accessory structures to the male reproductive system are known in several fami- lies of teleost, but their role in sperm production patterns and fertilization dynamics is still un- clear. The intraspecific variability in seminal vesicles, shown by the grass goby Zosterisessor ophiocephalus, presents an opportunity to examine both its possible correlation to alternative male mating tactics and the function of these accessory structures. In this species, males are known to release sperm in the form of sperm trails, bands of mucosubstances in which sperm are embedded. Surgical removal of seminal vesicles and histochemistry demonstrate that mucins, involved in the production of sperm trails, are secreted by the seminal vesicles. Gametes show a high longev- ity; sperm motility lasts on average 80 minutes. Eggs can be fertilized for several hours and do not need to be laid over trails because sperm are able to reach them via the surrounding water. Gonosomatic and seminal vesicle somatic indices, histology and histochemistry of gonads and seminal vesicles, sperm counts, and sperm trail longevity, suggest the presence of alternative male mating tactics in this species. Larger males have smaller testes and larger seminal vesicles compared to those of smaller males. The major role of seminal vesicles is mucin secretion in larger males, sperm storage in smaller ones. Trails of larger males last longer and release sperm more constantly over time than those of smaller males. Overall differences between males support the presence of differences in the intensity of sperm competition, with larger males performing nesting behaviour while smaller ones sneak spawnings. J. Exp. Zool. 283:81n 90, 1999.

On the mechanism of sperm release in three gobiid fishes (Teleostei: Gobiidae)

SynopsisIn fish, gamete release is commonly assumed to be synchronous in externally inseminating fishes. By collecting and counting the number of sperm and eggs released during separate matings in three demersal spawners, the mediterranean gobies, Zosterisessor ophiocephalus, Gobius niger, and Knipowitschia panizzae, we observed that gametes are released asynchronously. Males release sperm before females start laying their eggs. Sperm is released in the form of sperm trails laid on the nest surface; subsequently active spermatozoa leave the trails and move in the water for several minutes. Sperm trails consist of bands of viscous material in which sperm is embedded. In most cases eggs are not laid directly over the sperm trail, suggesting that sperm may contact the eggs after the latter are released in the water. Male sperm duct glands, seminal vesicles, known to secrete mucosubstances, are likely involved in the production of sperm trails. The possible influence of this mode of insemination on the mating style of marine gobies is discussed.

On Botulinum Neurotoxin Variability

ABSTRACT  The rapidly growing number of botulinum neurotoxin sequences poses the problem of the possible evolutionary significance of the variability of these superpotent neurotoxins for toxin-producing Clostridium species. To progress in the understanding of this remarkable phenomenon, we suggest that researchers should (i) abandon an anthropocentric view of these neurotoxins as human botulism-causing agents or as human therapeutics, (ii) begin to investigate in depth the role of botulinum neurotoxins in animal botulism in the wilderness, and (iii) devote large efforts to next-generation sequencing of soil samples to identify novel botulinum neurotoxins. In order to compare the fitness of the different toxins, we suggest that assays of all the steps from toxin production to animal death should be performed.

A male sexually dimorphic trait provides antimicrobials to eggs in blenny fish

Predation and microbial infections are the major causes of natural mortality for early life stages of oviparous species. The parental traits reducing the effects of predation are rather well described, whereas antimicrobial mechanisms enhancing offspring survival are largely unexplored. In this paper, we report that a male sexually dimorphic trait, the anal glands, of the redlip blenny (Ophioblennius atlanticus atlanticus) and the peacock blenny (Salaria pavo), two fish species with paternal egg care, produce a mucus enriched with antimicrobial substances. Histological and histochemical analyses showed that the anal glands of these species are characterized by the massive presence of mucus-secreting cells. Anal gland extracts, from both the hydrophilic and the hydrophobic protein fraction, exhibited a lysozyme-like activity. Field observations demonstrated that redlip blenny males, while performing egg care, rub the anal region over the nest internal surface, probably facilitating the transfer of mucus to eggs. These results strongly indicate that this sexually dimorphic trait is involved in egg defence against microbial infections.

Male Reproductive Apparatus of Some Blennioidei (Pisces: Teleostei)

I performed a comparative study of the morphology of the male genital apparatus on 11 species of blennies: Acanthemblemaria spinosa (Chaenopsidae), Enneanectes pectoralis, E. boelkei (Tripterygiidae), Gillellus rubrocinctus (Dactylopteridae), Labrisomus nuchipinnis, L. haitiensis, L. bucciferus, Paraclinus nigripinnis, Malacoctenus versicolor, M. triangulatus, and M. macropus (Labrisomidae). In the chaenopsid fish, an unpaired testis and a single seminal vesicle occurred. The seminal vesicle consisted of a single chamber containing no sperm and was filled with an homogeneous secretion. In the tripterygiid, dactyloscopid, and labrisomid species testes were paired, with a testicular gland interposed between the seminiferous lobules and the spermduct of each testis. Interspecific differences were noted in the volume of the testicular gland, relative to that of the testis, and in the development of the spermduct. Histochemical stainings in the testicular gland of Malacoctenus triangulatus and M. macropus revealed the secretion of glycogen and nonsulphated mucins. The possible involvement of the testicular gland, seminal vesicle, and spermduct in the nutrition of germ cells, production of a viscous seminal fluid and storage of sperm is discussed. B LENNIES (Pisces, Blennioidei) are a large group of smallish, elongate fishes characterized by a very flexible body. They are divided into six families, Blenniidae, Dactyloscopidae, Clinidae, Chaenopsidae, Labrisomidae, and Tripterygiidae, with about 675 recognized species (Nelson, 1984), most of which are common on coral reefs. As a group, their reproductive biology is well studied (Thresher, 1984), but the majority of work has centered on temperate subtidal species (Gibson, 1969; Patzner et al., 1986; de Jonge and Videler, 1989) with little known thus far about the more numerous reef

The biology of a population of spined loach, Cobitis taenia L.

Abstract A spined loach (Cobitis taenia L.) population inhabiting a small river in northern Italy was studied. At each age, females were larger than males and both sexes showed a marked seasonal pattern of growth with a high rate from May through November. Total population density averaged 2.38 ± 1.6 ind/m2 and the annual production in the study area was 3.3 g/m2. The first year class during the summer accounts for more than half the production. The sex‐ratio did not significantly depart from unity. Most individuals achieved sexual maturity in their second spring after hatching and spawning occurred in late May and June. The relationship between female total length and fecundity was lnF=l.07+0.065L. Males showing three different liveries were found throughout the year; the seasonal variation in their frequency suggested that males change livery in relation to their reproductive conditions.

The chromosomes of 16 molluscan species

Abstract Chromosome numbers were determined for two species of Placophora, eleven species of Gastropoda, one species of Pelecypoda and two species of Cephalopoda. No heterotypic or supernumerary chromosome resulted from the analysis of meiotic and, when possible, of mitotic chromosomes. For this reason no positive evidence emerges for the presence of differentiated sex chromosome pairs. Data available seem to indicate that evolution within the Mollusca phylum has been accompanied by a decrease in both chromosome number and DNA content (according to Hinegardner, 1974), if we consider subclasses, orders and families (apart from the subclass Prosobranchia). On the contrary the primitive class Placophora possesses a lower number of chromosomes than the Cephalopoda, which is the most specialized class.

Changes along the male reproductive axis in response to social context in a gonochoristic gobiid, Zosterisessor ophiocephalus (Teleostei, Gobiidae), with alternative mating tactics

Sexual selection has given rise, in several taxa, to intrasexual variation in male phenotype. While evolutionary studies have provided explanations of the adaptive function of this dramatic male phenotypic diversity, the proximate control of its expression has still to be completely understood. Several observations, primarily from sex-changing species, indicated a major role of social interactions in reproductive axis regulation and consequently in the expression of alternative male phenotypes. Here we documented changes along the male reproductive axis in response to social context in a gonochoristic species, the grass goby Zosterisessor ophiocephalus, where fully functional alternative male mating tactics appear to be expressed as an ontogenetic gradient. In the grass goby, larger and older males dig a nest and perform parental care, while smaller males sneak fertilization during territorial male spawning. Territorial males are characterized by a higher number of gonadotropin-releasing hormone (GnRH) neurons in forebrain preoptic area, smaller testes, larger seminal vesicles, and viscous ejaculates that last longer and contain fewer sperm than those of sneakers. To experimentally investigate the role of social factors in inducing changes along the male reproductive axis, sneakers were tested in two different situations: nesting alone or with ripe females. Sneakers that mated and performed parental care showed dramatic changes in brain, reproductive apparatus morphology, and ejaculate traits. GnRH-immunoreactive cells in forebrain preoptic area increased in number, reaching values typical of wild-caught parental males. Testes size decreased while seminal vesicle size increased and ejaculates showed lower sperm densities. These results were discussed within the framework of the social transduction hypothesis, which predicts that social experience should mediate, through a cascade of internal processes, shifts between morphs throughout life.