Mating Systems Flashcards
Aphids, parasitic wasps, mites, certain crustaceans, the majority of vascular plants all have what in common?
Do not reproduce sexually every generation
Cnemidophorus sp. (Whiptail lizards) Geckos Pocelliopsis sp. (stream fish) Snails Fungi and Protozoa
All of these have what in common?
They never reproduce sexually
The bellidoid rotigers, (small freshwater invertebrates) nerve reproduce asexually. This is an entire animal phylum that doesn’t
!
In whiptail lizards (6 of 15) what is required for the female to reproduce?
Another female courts her by a typically male pattern
What is the way in which some whiptail lizards reproduce called?
Pseudocopulation
T/F: nearly every eukaryote has a life history of sex
True
What mechanism would be capable of producing an adaptation like sex?
Natural Selection
Natural selection favors individuals that pass on their genes to the next generation, but in most species the males contribute nothing but sperm to reproduction
!
A parthenogenic (no fusion of male and female gametes) female should have the advantage, as shse passes on twice as many of her genes with each offspring
!
If there were a genetic polymorphism in a population, would asexual or sexual females have the enormous fitness advantage?
Asexual females, especially since in most species males contribute nothing but sperm
Sexual displays and rituals can be enormously expensive in terms of energy, time, and resources
Sex is expensive (preach)
Ex: male bower birds spend weeks constructing bowers solely for the purpose of attracting males
Ex: females are ridden by males after copulation, sometimes for many hours. It intereres with the foraging of the females and places them at increased risk of predation
Sex is expensive! (preach)
Ex: Tree frogs in Central America call to attract mates. Females are strongly attracted to the calls, it is much easier to get a mate if a frog invests a lot of time calling.
Carnivorous bats are also attracted to the calls, and they pluck the male right off the tree
Sex is dangerous!
Ex: Calling cricket males are more attractive but parasitic flies hone in on the sound and deposit their eggs into the singing males
Sex is dangerous!
There are a few very compelling reasons why species might benefit from sexual reproduction
The problem is that we lack a real understanding of how selection works at the species level. Natural selection, as we know it, works on _____ not species
alleles
Genes that act for the good of the species could be undermined by selfish mutations that crop up within the individuals and spread
!
The move comprehensive and persuasive mechanism for the existence of sex it the
Red Queen Hypothesis
A mechanism for the continued existence of sexual reproduction. Proposes that even species that do not seem to be changing are undergoing rapid evolution.
Red Queen Hypothesis
The natural world is so challenging that without constant evolution, species would go extinct. What provides the necessary variation that keeps evolution going? (2)
If not for these two things, all species would go extinct if environmental change were to occur
Sex and Recombination
Every species on the planet is locked in what JBS Haldane referre to as…
Evolutionary Arms Race
The natural enemies-parasites, predators, and competitors, of any species evolve every generation to better exploit their hosts, capture their pray, and push aside their competitors.
This produces a ____ among the hosts, prey and predators to negate these advantages
Selective Pressure
The Red Queen hypothesis is a natural outgrowth of the
Evolutionary Arms Race
Braconids parasitizing a hornworm larva
A harvestman parasitized by mites
Long-term evolutionary arms races are suggested in the
Fossil Record
For instance, in Cenozoic mammals, there is a correspondence between the fastest running herbivores and the fastest-running
Carnivores
The rise of jawed fishes seems to induce a cascade of shells, armor, and escape abilities among marine invertebrates in ancient, paleozoic seas.
Evolutionary Arms Race
In shorter time scales, apparent cases of evolutionary arms races are easy to find.
For instance, the rough-skinned newt, one of the most toxic amphibians on the planet, co-occurs with garter snakes that are just barely able to detoxify the poison.
Evolutionary Arms Race
The parasite-host arms race is documented on a gene for gene level in some cirumstances
Ex: the fungal parasite evolves quickley, and susceptible parasites are sitting ducks, only by constant evolution do the host survive, because the parasite cannot exploit a host with novel defenses
The stream fish, pocelliopsis in Mexico, asexual strains sufffer more or less parasitism than sexual individuals living in the same streams?
Much more parasitism for asexual strains
When genetic variation among sexual strains of pocelliopsis is lost, what happens to the advantage they had?
What does this imply?
The advantages is lost as well.
That genetic variability in sexual reproduction keeps parasites at bay.
A reason why an individual might benefit from reproducing sexually:
Sexual offspring will be more varied than asexual offspring. In an unchanging environment, this is a disadvantage, because the parental types were obviously successful enough to reproduce. In a changing environment, variable offspring ensure that at least a few will survive.
Bet-Hedging, reason why an individual might benefit from reproducing sexually
Offspring will be different from parents. If predators or pathogens are part of the environment, offspring which are different from their parents have an advantage, because pathogens are adapted to attack the parental generation.
Reason why an individual might benefit from reproducing sexually
Abundant evidence supports the notion that sex is advantageous in the face of environmental change. Many species that can switch between sexual and asexual reproduction turn to sex when faced with an imminent change in the environment.
!!
These engage in sex when conditions become unfavorable. Each spore stalk was formed from hundreds of independent ameboid cells that aggregated to form a sluglike organism, then differentiated into a stalk and spherical sphore case. The sphores will be carried away on air currents to new habitats and fuse to form diploid cells
Slime Molds
In ants, bees, wasps, some mites, sex is determined by the number of SETS of chromosomes
Males are ______ and descend from unfertilized eggs
Females are _____ and result from the genetic contribution of a mother and a father
Haploid
Diploid
Females of these species can either fertilize each egg, or let it remain unfertilized, thus controlling the sex of their offspring
Ants, bees, wasps, some mites
This sometimes results in sex ratios that are skewed in favor of ______, because mothers ensure that their sons will not compete with each other for mates by laying fewer male eggs.
female
For most turtles and alligators, the sex of an individual is determined by the incubation temperature of the eggs
Environmental Sex Determination
In many turtles, for instance, eggs that incubate at low temperatures become
females
and the eggs that incubate at high temperatures become
males
In some cases, sex can be determined by the social or physiological status of the individual. Small or poorly fed individuals are
larger individuals are
It can be vice versa. This pattern is especially common in sequential hermaphrodites
male
female
In humans, XX is female vs. XY male
In butterflies and birds, females are the
heterogametic sex (ZW, males are WW)
In XY chromosomal sex determination, the assortment of chromosomes during metaphase of Meosis I ensures that exactly half the male gametes contain X chromosomes, and exactly half contain Y.
This system produces 50% males and 50% females
In humans, there is actually a slight ____ bias at fertilization, because sperm containing Y chromosomes have a smaller “payload” and swim faster, thus resulting in more male zygotes.
male
