|
|
Některé reprodukční a fyziologické aspekty invasivních raků
YAZICIOGLU, Buket
Several studies have been carried out to understand reproductive biology of invasive crayfish. Many researchers have described how invasive species establish their population in new habitats, interactions between native and invasive species, their fast spreading, changing of behavior and biology especially reproductive behavior and even genetics. But it seems that there are still lots of questions and gaps which need to be addressed in case of invasive crayfish species. This thesis tried to focus on different aspects of reproduction biology of invasive crayfish. Generally, the normal crayfish reproduction mode is gonochorism. But, it has been showed in the literature that a few species such as Cherax quadricarinatus, Samastacus spinifrons, Parastacus virilastacus and Pacifastacus leniusculus may have different reproduction modes such as hermaphroditism or intersex. Parthenogenesis has been found in Procambarus fallax f. virginalis. Also, apomictic parthenogenesis has been reported in Orconectes limosus. Moreover, there have been several manipulations which directly affect reproduction biology of crayfish under lab conditions. Additionally, hybridization can be expected between Astacus astacus and Astacus leptodactylus, Orconectes rusticus and Orconectes propinquus under natural conditions. Some studies supposed that chemical factors also one of the reasons which could lead to some changes in reproductive system of crayfish. The objective of the Chapter 2 was to report first evidence of intersex in the signal crayfish, Pacifastacus leniusculus (Dana, 1852). That specimen appeared morphologically male but with both male and female genital openings, as well. Spermophores were obtained from vas defertia of this speciemen. Histological study was carried out and it has shown that both spermatophores and oocytes were present. The gonadosomatic index showed that intersex male had a GSI three times more higher than normal males. The ultrastructure of spermatozoa in three cambarid species Cambarus robustus, Orconectes propinquus, Orconectes rusticus were described and compered with eight previously studied species from family of Astacidae, Cambaridae and Parastacidae. In the studied cambarids, the crest-like protrusions in the anterior part of the acrosome is one of the most remarkable differences in case of morphological feature in spermatozoa and can be used for distinguishing the members of Cambaridae. The results of biometrical data showed that the smallest and biggest acrosome sizes in the studied species were in Parastacidae and Astacidae, respectively. The duration of post-mating spermatophore storage as well as the timing and temperature of spawning in two crayfish species (Pacifastacus leniusculus and Astacus astacus) were investigated in the Chapter 4. Seventy-one pairs of adult signal crayfish (Pacifastacus leniusculus) and thirty six pairs of noble crayfish (Astacus astacus) were used for experiment. The results indicated that there was a significant difference (P<0.05) between noble crayfish and signal crayfish in average duration of the post-mating spermatophore storage. The duration of the post-mating spermatophore storage is longer in the noble crayfish with 34.6 ? 1.7 days than the signal crayfish with 3.9 ? 0.5 days. There were also differences in the timing of mating and egg laying between the signal crayfish and noble crayfish. In the population of signal crayfish both mating and egg laying overlapped, but in the population of noble crayfish there was at least two weeks gap between last mating and first egg laying individuals. Water temperature was significantly (P<0.05) higher during mating and egg laying in the signal crayfish than the noble crayfish. The average temperatures for mating in both species were significantly (P<0.05) higher than the temperatures that they utilized for egg laying. As a conclusion more research is needed for better understand of the reproduction strategies in invasive crayfish.
|
guest ::
