Lecture 12: Human and animal Flashcards
What are the four questions that parents/future parents face, this is the life history theory?
How do they answer these questions
When to start breeding
How many offspring to produce
What sex offspring to produce
How much to care for offspring; which sex to care, which offspring to care for
They make tradeoffs, where they evaluate how limited the resources in their environment are
Describe Williams’ 1966 hypothesis about reproductive value
He formulated a formula that allows you to work out the RV of an organism. RV can be split into current and future reproduction. Current reproduction depends on fecundity (fertility/quality of offspring) and offspring survival, this is added to the future reproduction, which depends on the parents’ probability of survival, future fecundity and offspring survival.
List 3 types of tradeoffs
Growth vs reproduction
Offspring quantity vs quality
Current reproduction vs future
Discuss growth vs reproduction
An organism either invests its energy into somatic growth or reproductive effort. Reproductive value increases, then plateaus with age and survival decreases from birth. When the two lines meet on a graph, that’s when the organism should reproduce. Different animals mature at different ages (when their reproductive value is highest, for example male kudu mature at age 6 and females mature at 1 and a half.
What did Reznieck find about the age of maturation of predators that eat guppies?
The found that the predator that matured earlier, at adults guppies whereas the predator that matured later ate juvenile guppies. The ones that matured later had larger offspring size but lower reproductive effort.
Discuss offspring quality vs quantity, this comes under the question, how many offspring should be produced
Sinervo 1992 found that side blotched lizards produced more eggs, the lighter the eggs were, but this means their quality was reduced. Most eggs were medium weight and had the highest chance of survival in relation to mass. Birds have an optimum clutch size and they could produce more but they don’t because of tradeoffs with future survival and reproduction. The clutch size is where the benefit is highest and the cost is lower than the benefit.
Describe r and k selection
r selected species choose quantity over quality, they have the maximum rate of population increase and have high fecundity, small body size, short generations and early reproduction, e.g. trout
k selected species choose quality over quantity, they have maximum survival and reproduction when the population is at carrying capacity.
However this all relative; invertebrates are r selected over vertebrates, rodents are k selected over elephants and individuals within a species can be more or less k or r selected.
Describe teenage pregnancy in relation to quality
There is a correlation between teenage pregnancies and poor quality upbringing. It’s associated with poverty and although the government have tried to reduce it, they’ve had no effect. Instead, they educate the children about sex at an earlier age to try and prevent it. Low education, no father and were usually small at birth.
Discuss what sex offspring should be produced
There is a conflict of interest here, Fisher argued that the sex ratio should be 1:1 however this is not the case. Only the queen in a colony wants a 1:1 ratio, the sisters want a 3:1 ratio. This conflict of interest was discovered by Trivers. The workers/sisters usually win as they control egg nourishment. Bateman then came up with the theory that males have more variance in reproductive success than females. A male in a good condition will outreproduce a female but if both are in poor condition, the female will outreproduce. This is adaptive sex ratio biasing, also know as the Trivers-Willard effect.
Describe the trivers-willard effect
The parents should invest in males if they’re in good condition and invest in females if they’re in poor condition. This supports the 1:1 fisherian sex ratio, but it can move away from this depedning on the benefits/costs. The condition of the young correlates with the condition of the parent during parental investment, this condition will continue through to adulthood. The differences in condition cause greater differences for the reproductive success of males compared to females. Clutton-Brock supported this. Altman found this effect but reversed, the lower the maternal rank, the more males and vice versa.
This also relates to sequential hermaphroditism, when blue headed wrasse reach a certain size, they turn from females to males.
Discuss helpers at the nest
Komdeur 1997 found that 88% of female warlbers help but the sons disperse. Mothers in high quality territories overproduce daughters, low quality nests over produce sons. This shifted when translocated. However, when there is one helper, most of the offspring are daughters but when there’s two helpers, most are sons. If the helpers are removed, most are daughters. This also happens with food availability with possums and with zebra finches; attractive parents produce more same sex offspring compared to unattractive who produce opposite sex offspring.
How do parents care for their offspring?
How do they know how much care to give their offspring?
Parents care for their children by maintaining the nest, producing gametes, protecting the zygotes, providing food and warmth, caring for nutritional independence. It increases the reproductive potential of the offspring at a cost to the parent.
They can’t overly care as there are many costs of parenting. It costs energy; reptile eggs can account for 20% of the annual energy budget. Some frogs lose up to 20% of their body weight when guarding eggs. It puts you at increased risk of predation, increased parasite load and lost time.
Trivers found that there is parental offspring conflict; offspring want maximum benefit however this can kill or overexhaust the mother, there is a weaning effect in cats where the mother doesn’t respond to increased initiation of offspring suckling and she escapes to a shelf.
Describe sibling rivalry
Also describe nestling begging
This supports the parent offspring conflict model. Each offspring wants more parental investment for itself so offspring manipulate the parents. For example, they beg (scramble competition), the begging is costly (increased risk of predation) but the louder the beg the more likely that chick will be fed as the intensity of begging signifies need. Godfray 1991.
Kilner 1997 found that hungrier birds beg for longer but it could be manipulated to get more food as parents provision the food depending on the intensity.
Describe genomic conflict/genomic imprinting
It has been found that some fathers induce their offspring to ask the mother for more resources, more than she is willing to give as the mother’s further production isn’t important to the father. The mother tries to silence the genes but over time they become imprinted so demand genes are only expressed if inherited by the father and defence genes vice versa.
This also happens in mice the lgf2 gene which is expressed via the paternal copy but suppressed by the maternal. This gene promotes the acquisition of resources from the mother in the placenta. This was manipulated, when activated, the mice have 30% higher than normal birth weight.
Who cares for the offspring?
There are 4 options; One parent (mother or father), no parent, both parents (this is rare) or others (related or unrelated). Maynard and Smith made an evolutionary stable strategy model of investment. W=No. of eggs laid by deserting female. w=no. laid by caring female. P1/P2/P0= probability of offspring survival when cared by 2, 1 or 0 parents. p= probability of male mating again. Both sexes desert if WP0 is more likely than wP1 and P0(1+p) (aka woman stays father leaves), which is more likely than P1. Only the female deserts if WP1>wP2+P1>P0(1+p). Only male deserts if wP1>WP0+P1(1+p)>P2. Both care if wP2>WP1+P2>P1(1+p). In many species off fish the males look after the eggs and the females look to lay more eggs. Whereas in mammals, males gain more if they seek extra matings. In birds two parents are usually needed and EPCs are unlikely. So basically, they looked after the offspring if it’s most beneficial
