VL 10 Flashcards
How to find a mate?
On the sites where females lay their eggs – eg. Fruit flies on fruit, scatophagid flies on dung
Visual (eg. fireflies), pheromone, or acoustic (eg. cricket) signals
Assembling at landmarks – gatherings on tops of hills, or walls, or landmarks – leks (eg. midges)
Fight for one – males assemble where females visit and fight for access – rhinoceros and dung beetles – enlarged weapons or sneaky strategies
As quickly as possible, to avoid competition…
* In many species, males will wait for females to emerge to immediately mate them – frequently their own siblings. Some species of bees, wasps, ants, butterflies, beetles and parasitoids.
Acoustic signals when finding a mate
Mosquitoes pair with mates based on wingbeat frequency
Males and female frequencies converge, whereas two of the same sex become dissonant
Sex
Males can produce a packet of sperm called a spermatophore
Males will have a reproductive organ of a specific shape to interlock
with the female
Females have a spermatheca, where they store sperm – some mate but can then use sperm later. Ie. Honey bee queens mate for 1 day, then lay hundreds of thousands of eggs over 2-3 years using the sperm
Most insects oviposit eggs (oviparous), but some retain the offspring until they give birth to live young (viviparous) – tsetse flies
Some insects do not always reproduce sexually. Can reproduce through parthenogenesis (no fertilization) such as aphids – clones of mother. Or hymenopterans (eg. wasps, bees and ants), producing male, haploid workers from unfertilized eggs.
Types of sexual selection
Epigamic (between genders): criteria used to choose high quality mate pre-copulation. Female choice drives male features.
Intrasexual (within gender, usually males): ability to secure a mate
- Pre copulatory – finding, signals, territory defense, fighting ability
- Post copulatory – mate guarding, preventing further mating
Sex ratio bias or high male investment can alter dynamics
Enlarged weapon - Rhinocerous Beetle
Different sexual selection pressure in different countries dependant on resource availability
Costs:
* Requires higher muscle mass
* Longer development time
* Impedes foraging and escape
Sexual dimprphism
males are morphologically distinct from females ie. have a horn
Male dimorphism
there are different male morphologies within a population that take advantage of different mating strategies
Alternative / sneaky strategies: giraffe weevil
Smaller males use stealth to avoid fighting
Insert themselves between mating pair to disrupt
Nuptial gift - cheating
In some cricket species, the spermatophlax can stimulate eating but have low nutritional value
Bittacus scorpionfly males try and steal the gifts back after sex
Male Hilara and Empis dance flies may offer fake gifts rather than prey
Sexual conflict
Female:
Gains reproductive fitness if she mates more than once – increased genetic diversity in offspring
Male:
Loses reproductive fitness if the female mates with other males
different sexual conflicts
pages 22 - 24
Degree of investment of parental care
The higher the investment, the greater the fitness of the offspring at the expense of future reproduction
High investment = higher chance of individual offspring surviving
Low investment = parental insect has more resources for survival and
future reproduction
Evolutionary drivers of high parental care: harsh environments, ephemeral food sources or natural enemy pressure
Inclusive fitness
Inclusive fitness = direct + indirect fitness
Even actions which reduce the fitness of the insect and the chance of future reproduction may still have a net benefit
Two examples of egg maintenaance and guarding
Giant waterbug
* Female lays eggs on male’s back
* Egg guarding
* Dessication prevention and egg aeration
Earwig
* Egg grooming reduces mold formation
* Females will move eggs to a new nest if there is flooding or dessication
* Egg guarding prevents cannibalization
Biparental care: Burying beetles
Food store
Build nest chamber
Feeding offspring
Defense against predators
