Lecture 18 Flashcards
The phenotype. . .
is a combination between both genotype & environment
Reproduction is. . .
the means by which a new organism acquires a genotype
Asexual vs Sexual females
- asexual females can produce twice as many childbearing offspring (females) as sexual females, so natural selection might be expected to favour asexual reproduction
Asexual species are more common in agricultural habitats that are typically. . .
homogenous
perhaps sexual reproduction provides advantages in spatially and temporally variable environments
asexual reproduction - will favour species that don’t require sex in order to deal with the changing environments
Define dimorphic
occurring in or representing two distinct forms.
sexual dimorphism = differences between the sexes
A signalling explanation why gametes (sperm & eggs) are dimorphic
- prevents the ligands from binding to receptors on its own membrane which may impair intercellular signalling
- producing ligand and receptor in an asymmetric manner resolves this issue
1 challenge in sexual reproduction
introduces the challenge of bringing male and female gametes together
signals, indicating location and receptivity, are required to bring sexes (or gametes) together - this can also act as CUES to alert natural enemies
Modes of reproduction that remove the hassle with sex
facultative parthenogenesis
hermaphroditism
Facultative parthenogenesis
females are able to produce viable eggs irrespective of whether mating has taken place
hermaphroditism
organisms have complete or partial reproductive organs and produces gametes normally associated with both male and female sexes
What is sexual selection?
when there is competition between members of one sex (typically males) for reproductive opportunities with the other sex (typically females)
signalling
males have evolved armaments that are used in contests & may also signal fighting ability
Darwin also suggested that sexual selection shapes “organs of sense”
- chemical signalling (pheromones) and the function of antennae were not discovered until many years later
Traps with a single female, which release less pheromone than traps with 2 females,. . .
attract males with larger antennae
Reproductive success for a female can be improved by mating with . . .
more than 1 male (polyandry) within their reproductive cycle
Reproductive success for males is compromized by. . .
polyandry, and sexual selection favours mechanisms to prevent it
How might females benefit from polyandry?
If competitive fertilization success is heritable, females may benefit from polyandry by producing sons that are superior sperm competitors
acquisition of sufficient sperm to fertilise all of a female’s ova
Male counter-adaptations to polyandry
- males may physically prevent her from mating
- males of many butterflies protect their paternity with a sphragis (dried seminal fluid that covers the female genital opening, preventing other males from mating)
- interfering with female signalling
female spiders place a pheromone in their webs to attract males - attracted males destroy her web before courtship
Polyandry vs polygyny
polyandry - the best outcome for females
polygyny - the best outcome for males
The net benefit for the female may not be the same as that for the offspring. Why?
Because the maximal benefit for the offspring may require a higher cost for the mother, which could limit the mother’s ability to survive until the next reproductive season.
What is meant by cooperative breeding?
the dependent young receive parental care (food, defense) from their parents as well as other individuals in the group
What are the major defining features of eusocial insects?
1) cooperative care of young
2) sterile castes - help in nest maintenance and raising offspring, but cannot themselves reproduce
3) overlapping generations - such that mother, adult offspring and larval offspring are alive at the same time
e.g. wasps, ants, bees
Complex societies require the exchange and acquisition of lots of info
- green tree ants cooperate to construct a lead
- scouting worker bees return to the nest and perform a dance, which tells other bees the location, distance, and nature of the food source
