Evidence Of Hermaphroditism Research Articles

Reproductive cycle, fecundity and growth of the freshwater mussel Unio tumidus (Bivalvia: Unionidae) from Lake Viinijärvi, Finland

ABSTRACT Freshwater mussels have a substantial role in aquatic ecosystem function and provide valuable ecosystem services, including water filtration, nutrient cycling, habitat creation and sediment stabilization. While they face population declines globally that can negatively affect an ecosystem's health, such as reducing the water quality and increasing the turbidity, lack of information about the basic reproductive biology for most species makes their conservation much more difficult. Here, we monitored a population of Unio tumidus for a year to study its reproductive biology, gonad-dwelling parasites and growth rate in Lake Viinijärvi, Finland. Our data revealed that this species was dioecious with no evidence of hermaphroditism and was non-significantly female-biased (a male to female ratio of 1:1.3). Both sexes of U. tumidus had continuous gametogenesis during the study period with two peaks in the gonadosomatic index (GSI%) during November and May, followed by two clear declines in December and June. Gravidity period (brooding) of embryos or glochidia in the female's outer gills lasted from June to July. Therefore, this population of U. tumidus can be classified as a short-term breeder (tachytictic). The clear decline of GSI% in December might be a strategy that individuals of U. tumidus use to resorb resources back from the gonad for somatic maintenance during winter. Mean length of glochidia was 391 ± 0.049 µm, being among the largest known glochidia for Unionidae. No gonad-dwelling trematode parasites were detected and the population exhibited high fecundity (numbers of oocytes per female), with an average oocyte production of 242,000 ± 18,000. The studied population had a moderate growth rate with a maximum predicted age of 13 years and asymptotic length (the length at which growth slows down while the mussel continues to age, L∞) of 114 mm. Our study provides the first quantitative data and histological analysis of the reproductive biology of U. tumidus, serving as a basis for future research and conservation.

Rapid Reproductive Analysis and Length-Dependent Relationships of Lutjanus biguttatus (Perciformes: Lutjanidae) from Papua New Guinea

We describe a simple, inexpensive method for field-based histological analysis of fish gonads, and we used this method to describe the reproductive biology of the small snapper Lutjanus biguttatus from a remote area in Papua New Guinea (i.e., where laboratory equipment is limited and electrical service is lacking). We estimate male L50 at 13 cm FL and female L50 at 17 cm FL. Sex ratio is not significantly different from 1 : 1. There is no evidence for hermaphroditism. Fork length is a linear function of total length, FL = -0.1823 0.9647(TL), and weight is a cubic function of fork length, W = 0.0129(FL)3.0049. This information was generated during a 2-week period when the majority of our time was occupied by fish surveys. Our analyses were limited by availability of specimens (not processing time); therefore the methods we employed can help fill one of the information voids that preclude life-history-based management of coral-reef fishes.

LIFE HISTORY CHARACTERISTICS OFTHERMOSPHAEROMA THERMOPHILUM, THE SOCORRO ISOPOD (CRUSTACEA: PERACARIDA)

The endangered species (Federal endangered species list), Thermosphaeroma thermophilum, or "Socorro Isopod," is endemic to a small spring near Socorro, New Mexico, that is thermally stable year-round. Isopods were observed in the field, and monthly samples were collected between March 1978 and February 1979 for laboratory examination. Males were larger than females, and sex ratio in the habitat was consistently biased toward males, particularly when sexually receptive females were abundant. Reproduction occurred primarily, although not exclusively, in spring and fall. Food seemed scarce, and intense predation by the omnivorous isopods appeared to exclude most invertebrate species, including predaceous aquatic insects, from the habitat. Fish do not inhabit the spring and avian predation is minimal or non-existent, perhaps permitting isopods to reach high densities and decreasing risks associated with male mate-searching behavior. Field and laboratory data indicated that isopods live less than 1 year. Males grow and reach sexual maturity faster than females. No evidence of hermaphroditism or sex-change was observed. Females were iteroparous and brood size increased with a female's age, but females were small and varied little in size, suggesting selection for an optimal female size.

Cytology and Reproduction of Helicotylenchus Dihystera and H. Erythrinae 1)

Several populations of the monosexual species Helscotylenchus dihystera were studied with respect to their chromosomal complement and mode of reproduction to clarify the question of digonic hermaphroditism. No synapsis of homologous chromosomes takes place and maturation consists of a single mitotic division. The somatic chromosome number observed at anaphase or telophase of the maturation division and at prometaphase of the first cleavage division was 2n = 38 in two populations from North Carolina (with possible variation from 38 to 40), 2n = 34 in one population from North Carolina, and 2n = 30 in two populations from Wisconsin. Cleavage proceeded without fertilization. Reproduction in H. dihystera is, therefore, by mitotic parthenogenesis; there is no evidence of hermaphroditism. Cytology and reproduction were also studied in a single population of the bisexual species H. erythrinae from North Carolina. Synapsis of homologous chromosomes takes place, and maturation is normal, consisting of two divisions. The somatic chromosome number observed at prometaphase of oogonial divisions is 2n = 10 and the reduced chromosome number seen at anaphase of the first maturation division and metaphase of the second maturation division of oocytes is n = 5. Re-establishment of the somatic chromosome number takes place through fertilization. No substantial differences in size and shape of the chromosomes of these two species were observed. This is interpreted as indicating the existence of polyploidy in H. dihystera.

Hermaphroditic Female Schistosomatium douthitti (Trematoda: Schistosomatidae)

In trematodes of the family Schistosomatidae it has long been considered that there is complete separation of sexes, in contrast to the hermaphroditic condition occurring in other families of flukes. However, recent reports on hermaphroditic tendencies in males of the genus Schistosoma (Vogel, 1947; Short, 1948a; Gonnert, 1949; and Lagrange and Scheecqmans, 1949) indicate that sex separation is not always complete in this genus. Observations reported in the present paper show that in the genus Schistosomatium, also, separation of sexes is not always complete. During a study to be reported elsewhere (in press), the writer had occasion to examine a large number of stained male and female Schistosomatium douthitti from deer mice. These were searched carefully for any evidence of hermaphroditism, with the result that certain females were observed to possess, besides ovaries, discrete cellular bodies which on further study proved to be immature testicular follicles. The present paper is concerned with these hermaphroditic females.