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stress related suppression hypothesis
dominants render subordinate infertile, induce chronic stress, compromises fertility. continual activation of HPA axis, chronic elevation of glucocorticoid adrenal hormone.
single dominant female breeds- produces 80% of pups, dom attacks subs one month before giving birth. drives them from group until the litter is born. they cannot forage or sleep with the group
young et al 2006
9 years of detailed life history and behaviour and physiological monitoring data. evicted subordinates- 2 fold increases in faecal GC metabolite levels, down regulated repro physiology, reduce conception rates, increased abortion rates. GC levels increased due to stress of living away from group- down regulation of pituitary sensitivity to GnRH and disruption of oocyte maturation. they were more likely to evict subs with whom repro conflict was most likely to be acute
what are the benefits to meerkats for evicting subs
reduces chance that litters will have to compete for ltd amount of care in group, ratio of helpers to litter associated w increased survival. reduces threat of infanticide by sub females, only commit it when they are pregnant, only likely up to four days of litter's life, evictees return by third day. breeding female also reduces prenatal investment in offspring, altrical births can result as she retains energy for multiple repros per year.
Barret et al 90
marmosets- dominate female breeds, others anovulatory. olfactory cues from dom- maintain suppression
hacklander et al 2003
alpine marmots- only dom females repro, initiators of agonistic interactions to subs. subs higher GCs during gestation periods. interferes w stimulatory action of gonadotropins on sex-steroid producing and decreases pituitary responsiveness to GnRH. sub females- basal concentration of circulating progesterone. ADV of keeping no of adults in group high is due to increased heat during hibernation- increased survival rate of juveniles. costs to suppressing repro= more subs in group lower probability of dominant repro'ing successfully.
dominant female only one who can have litter- subs regained access to group if they aborted their litter - might be due to stress or a proximate mechanism to regain entry.
repro skew- evenness with which repro is distributed in group. concession models- subs only remain in group if they have immediate fitness incentives to do so, dominants have full control over breeding, may gain from relinquishing share of repro to subs to induce them to stay. do doms have perfect control?- do subs repro simply because doms cant stop them. long lived animals= benefit from delayed dispersal regardless of whether it is in the dom's interest- when dominant evicts subs, they are reluctant to leave. alternative concession model- eviction threat= only way to control sub repro. subs selected to exercise restraint so as not to trigger eviction.
2 modes of eviction: groups of males and females face intense aggression from other group members/ same sex groups left voluntarily. eviction to reduce overly large groups (group size not correlated with survival). increase in no of potential breeders= cause for eviction? both evictions during oestrus- direct comp with breeders. females evicted other females that would've been sexually mature in six months. eviction may be only way of regulating young born in group- dom has little/ no ability to suppress repro
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