Evolution during millions of years in perpetual darkness leads to mutations in non-visual opsin genes (Melanopsin and TMT opsin) and an aberrant, blind circadian clock in cavefish.
1. In the last decade, many attempts have been made to contain the spread of the North American crayfish Procambarus clarkii, an invader of many European water bodies, but none has been successful. 2. This study investigates the effects that ionising irradiation has on the reproduction of P. clarkii males by analysing the behaviour of the treated individuals, their reproductive output, the vitality and survival of their offspring and the damages induced to their gonads. 3. We found that a dose of 20 Gy X-rays did not compromise either the survival or the mating ability of males, but reduced the size of their testes and significantly altered spermatogenesis. The number of aborted eggs was larger in clutches sired by treated males, with a consequent reduction (by 43%) in the number of offspring. 4. These results foster hopes in our efforts to control invasive crayfish, showing the potential effectiveness of ionising irradiation to reduce male fertility in the perspective of adopting the Sterile Male Release Technique to control P. clarkii populations.
The blind cave-dwelling fish Phreatichthys andruzzii shows rapid eye development, and at a temperature of 29.5°C, maximal eye differentiation is reached 36 h after egg laying. Very rapid eye degeneration then occurs, and a rudimentary and very degenerated ocular cyst is all that remains 1 month later. This may explain why this species has so often been erroneously considered anophthalmic. Ocular degeneration starts with a decrease in the rate of mitosis in the neuroblastic cells of the retinal Anlage. Degeneration by means of lytic processes is clearly observed beginning 32 h after egg laying. Disappearance of the lens, transformation of the cornea into skin, and cryptic degeneration of the eyes are phenotypic variations of the fundamental mechanisms of eye development in vertebrates. These can be considered evolutionary adaptations by the ancestral fishes to the aphotic cave environment.
The phylogenetic relationships of two cavefish, Phreatichthys andruzzii and Garra barreimiae, belonging to the family Cyprinidae, were investigated by sequencing the mitochondrial cytochrome b gene. These cavefish species are native to Somalia (eastern Africa) and Oman (southeastern Arabian peninsula), respectively, and so far no molecular support to their taxonomy and phylogenetic position was ever provided. The analysis of cytochrome b sequences showed that the species are monophyletic taxa, closely related to each other and to other species of the genus Garra. Molecular clock calculations allowed to date the origin of these hypogaean species back to the Plio-Pleistocene and support the hypothesis that African cyprinids originated from Miocenic immigrations of Asian ancestors.
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