Shark Reproduction Flashcards
What influenced the evolutionary success of chondrichthyans?
wide range of reproductive strategies
What are the roles of estrogens in reproduction?
- stimulate vitellogenesis and the hepatic synthesis of yolk
- stimulate the development of different parts of the reproductive tract in females (oviducal gland)
- sperm storage
- secretion of maternal nutrients
- role in prepping uterus for parturition by stimulating relaxin production
- role in passage of eggs into uterus (enlarge isthmus)
What are the roles of androgens in female reproduction?
precursor to estrogens
-sperm storage
lecithotrophy
entire embryonic development is supported solely be yolk-sace
matrotrophy
at least part of embryo development is supported by additional maternal input of nutrients
oviparity
external embryonic development
viviparity
internal embryonic development
oviparous
lecithotrophic, lay eggs
yolk sac viviparous
lecithotrophic, embryos solely nourished by yolk sac but develop within mothers uterus
histotrophy
developing embryos receive additional nutrition in the form of uterine secretions
oophagy
embryos feed on unfertilized eggs produced by the ovary
adelphophagy
first hatch embryo eats other embryos, then unfertilized eggs
placental viviparity
placental connection links embryo to mother and provides nutrition
What hormone is produced by the hypothalamus?
gonadotropin releasing hormone (GnRH)
What hormones are produced in the pituitary?
- gonadotropin hormones (GTH)
- follicle stimulating hormone and luteinizing hormone
What is the role of GnRH?
- stimulate production of GTH in pituitary
- direct influence on steroid hormone production in gonads
What is the role of GTHs?
- stimulate gametogenesis
- stimulate synthesis of steroid hormones in gonads
What is needed for GnRH to exert any functions?
The presence of a receptor at the target tissue
-binds to G-protein-coupled receptor GnRHR
What is the role of follicle stimulating hormone?
associated with early stages of gonadal growth
What is the role of luteinizing hormone?
regulates maturational events
What are the primary gonadal steroids involved in reproduction?
- 17beta-Estradiol
- Progesterone
- Testosterone
What is the source of E2 and T?
granulosa and theca cells of ovarian follicles
What is the primary source of P4?
Corpora lutea
-also produced in granulosa cells
What is the primary source of T in males?
Sertoli cells, with less contribution from Leydig cells
Describe the female reproductive system
-single or paired ovary associated with epigonal organ (immune function)
-paired oviducts
-ostium
-oviducal gland
-isthmus
-uterus
-cervix
cloaca
What is the role of the oviducal gland?
- egg fertilization
- secrete egg capsules
- sperm storage
What are the roles of P4?
- downregulate synthesis of vitellogenin to stimulate the maturation of ovarian follicles that have completed vitellogenesis
- suppress E2
- increase during preovulatory period and remain elevated in initial stage of pregnancy
- maintenance of pregnancy (decrease contractions during early pregnancy)
Describe the male reproductive tract.
- paired testes in epigonal organ
- ductus efferens
- epididymis
- vas deferens
- leydig glands
- seminal vesicles
Where does sperm storage occur in males?
epididymis
What is the role of T in males?
spermatogenesis
- development and maturation of spermatocyts
- maturation
What is the role of relaxin?
- prep female for parturition (widen cervix, uterine contractions)
- in male semen to cause contractions to help sperm move to eggs
What are the basic reproductive parameters required for management?
- size at maturity (ensure sufficient reproductive individuals are maintained in population)
- reproductive cycle
- spatial patterns of reproduction (minimize impact on pupping)
- fertility (# pups)
Why would knowing spatial and temporal timing of reproductive events benefit management?
ensure the fishing activities are minimized during reproductive events
-identification of the roles that habitats/locations play for different stages of the reproductive cycle is critical
What triggers the sexual maturation of sharks?
gonadotropin hormones (follicle stimulating hormone and luteinizing hormone)
synchronous
all individuals in the same reproductive stage (vitellogenesis, gestation, resting) go through the same reproductive events at the same time of the year
What is a sign that parturition just occurred?
- elongated ovaries with small, non-vitellogenic, whiteish follicles
- flaccid uterus
ostium
cilia move ova from the ovary into the ostium, which leads to the oviduct
isthmus
region connecting the oviducal gland to the uterus
-morphological changes in this region during ovulatory cycle may be under control of P4
uterus
- house developing embryos in viviparous species
- sclerotization for oviparous species (development of properties for egg case hardening)
What determines length of reproductive cycle and gestation?
how effectively the mother can sequester energy from the environment and transfer it to the developing oocytes or embryos and the mode of embryonic nutrition
asynchronous
all females can be at different stages of the reproductive cycle
- no seasonality
- generally tropical species with stable environmental conditions and prey year round
Which ovary is active in lamnid?
Only the right ovary
How is the lamnid ovary different from other groups?
- morphology optimizes ova production and high ovulation rates
- series of internal cavities to increase surface area to generate oocytes
- a pocket or efferent ovarian pore opens to the abdominal cavity and allows ovulated ova to escape to the ostium
Where does fertilization take place in lamnids?
Might be anterior oviduct rather than oviducal gland
What is the primary source of fetal nutrition in lamnids?
unfertilized ova densely packed in ovoid egg capsules
Describe embryo consumption of eggs in lamnids.
yolk packs into a distended stomach and then the embryo gets nutrition for the rest of gestation by digesting the consumed yolk in the distended stomach
What controls migrations in pregnant lamnids?
must reside in locations where sufficient resources are available for foraging and yolk production
-in pelagic species this may require migration with potential prey or to locations where prey aggregate seasonally
How is uterus adapted for viviparity?
- folds to increase surface area for respiratory exchange
- increased vascularity
- thinning of epithelium
- epithelium good from osmoregulation, H2O transport, O2 delivery, CO2 removal
What is the criteria for a shark nursery area?
- sharks are more commonly encountered in the area than other areas
- sharks have a tendency to remain or return for extended periods
- the area or habitat is repeatedly used across years
primary nursery
where sharks give birth or lay eggs
secondary nursery
where juveniles spend years as they grow towards maturity
What are common assumptions about shark nursery areas?
- all sharks have nursery areas (no true)
- nursery areas provide ample resources (not always true, trade off between food and predation risk)
- nursery areas reduce predation risk and have low mortality rates (not always true)
- primary nurseries overlap with secondary nurseries
Why do we often focus on shark nursery grounds?
- often neonates and young juveniles considered most critical life stage (not necessarily true)
- difficulty management adules with expansive home ranges
What life stage is often most important to population maintenance?
juveniles nearing maturity
Why might tiger beach be used by female sharks?
- calm warm waters year-round may reduce gestation and accelerate embryonic development
- reduce mating harassment
What is the problem with aggregations of gravid females?
fishing aggregations may pose significant threat to viability and health of local and regional populations
