118 research outputs found
A standardized terminology for describing reproductive development in fishes
19 pĂĄginas, 12 figuras, 3 tablas.-- Open access journalAs the number of fish reproduction studies has proliferated, so has the number of gonadal classification schemes
and terms. This has made it difficult for both scientists and resource managers to communicate and for comparisons to
be made among studies.We propose the adoption of a simple, universal terminology for the phases in the reproductive
cycle, which can be applied to all male and female elasmobranch and teleost fishes. These phases were chosen because
they define key milestones in the reproductive cycle; the phases include immature, developing, spawning capable,
regressing, and regenerating. Although the temporal sequence of events during gamete development in each phase
may vary among species, each phase has specific histological and physiological markers and is conceptually universal.
The immature phase can occur only once. The developing phase signals entry into the gonadotropin-dependent stage
of oogenesis and spermatogenesis and ultimately results in gonadal growth. The spawning capable phase includes (1)
those fish with gamete development that is sufficiently advanced to allow for spawning within the current reproductive
cycle and (2) batch-spawning females that show signs of previous spawns (i.e., postovulatory follicle complex) and
that are also capable of additional spawns during the current cycle. Within the spawning capable phase, an actively
spawning subphase is defined that corresponds to hydration and ovulation in females and spermiation in males. The
regressing phase indicates completion of the reproductive cycle and, for many fish, completion of the spawning season.
Fish in the regenerating phase are sexually mature but reproductively inactive. Species-specific histological criteria
or classes can be incorporated within each of the universal phases, allowing for more specific divisions (subphases) while preserving the overall reproductive terminology for comparative purposes. This terminology can easily be
modified for fishes with alternate reproductive strategies, such as hermaphrodites (addition of a transition phase) and
livebearers (addition of a gestation phase)Fish Reproduction and Fisheries (FRESH; European
Cooperation in Science and Technology Action FA0601)
and theWest Palm Beach Fishing Club (Florida) provided funding
for the gonadal histology workshops where this terminology
was developed and refined. Additionally, we thank FRESH for
travel and publication fundsPeer reviewe
Evidence of positive selection associated with placental loss in tiger sharks
Background: All vertebrates initially feed their offspring using yolk reserves. In some live-bearing species these yolk
reserves may be supplemented with extra nutrition via a placenta. Sharks belonging to the Carcharhinidae family
are all live-bearing, and with the exception of the tiger shark (Galeocerdo cuvier), develop placental connections
after exhausting yolk reserves. Phylogenetic relationships suggest the lack of placenta in tiger sharks is due to
secondary loss. This represents a dramatic shift in reproductive strategy, and is likely to have left a molecular
footprint of positive selection within the genome.
Results: We sequenced the transcriptome of the tiger shark and eight other live-bearing shark species. From this
data we constructed a time-calibrated phylogenetic tree estimating the tiger shark lineage diverged from the
placental carcharhinids approximately 94 million years ago. Along the tiger shark lineage, we identified five genes
exhibiting a signature of positive selection. Four of these genes have functions likely associated with brain
development (YWHAE and ARL6IP5) and sexual reproduction (VAMP4 and TCTEX1D2).
Conclusions: Our results indicate the loss of placenta in tiger sharks may be associated with subsequent adaptive
changes in brain development and sperm production
Multiple paternity in a viviparous toad with internal fertilisation
Anurans are renowned for a high diversity of reproductive modes, but less than 1% of species exhibit internal fertilisation followed by viviparity. In the live bearing West African Nimba toad (Nimbaphrynoides occidentalis), females produce yolk-poor eggs and internally nourish their young after fertilisation. Birth of fully developed juveniles takes place after nine months. In the present study, we used genetic markers (eight microsatellite loci) to assign the paternity of litters of 12 females comprising on average 9.7 juveniles. In nine out of twelve families (75%) a single sire was sufficient; in three families (25%) more than one sire was necessary to explain the observed genotypes in each family. These findings are backed up with field observations of male resource defence (underground cavities in which mating takes place) as well as coercive mating attempts, suggesting that the observed moderate level of multiple paternity in a species without distinct sperm storage organs is governed by a balance of female mate choice and male reproductive strategies
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