Insect 2nd

Insect 2nd

1. Parasitoids, Hyperparasitoids, multiple levels, ectoparasitoids and endoparasitoids, solitary and gregarious

   • Iodoiobionts: host paralysed and doesn't grow, often dies, in protected situation, less specificity, wide host range, ancestral
   • Koinobionts: both alive, host grows, feed and protects itself, parasitoid benefits from this, more derived strategy, host specificity, closer arms race, cost to life, Dinocampus concinellae, braconid wasp and ladybird
     • Hymenoptera = order with most parasitoids, ovipositors and stings,
       • Host descrimination, all adults mark host, why? combination of reasons 2,3 and 4, help relatives, avoid superparasitism, all do it so all benefit, superparasitism different to hyperparasitism, second batch die, attack or suppression
       • Host location: tri-trophic interactions, synomones, volatiles = communication, cues, ovipositor, mechanical damage and secretion, voliticin from beet armyworm
         • Important in biological control: Casava and mealybug
   • Arms race: based on fecundicity
     • Host defence: initial defence AVOID (only option for idoiobionts), green cloverworm, response to being parasitized, FIGHT OFF encapsulation, haematocyte cells, oxygen starved, behavioural responses, Drosophila and ethanol, example of active resistance
       • Resistance has benefits but also costs: often neglected in models active or standing resistance,
         • Engaged in evolutionary arms race with hosts
     • Avoid encapsulation (niche), subversion (pierce), attack - venoms (ectoparasites and all idoiobionts), teratocyte cells around embryo, steal resourcs or weake immune system, polyDNA virus (virus prevents encapsulation), EVIDENCE by washing eggs
       • Polyembryony shows how parasitoid resistance also has costs

2. Sex and reproduction

   • How might extreme sex ratios arise
     • Haplodiploidy: female control, Hymenoptera, diploid eggs female, haploid male, single sex determining locus, heterozygous = female, homozygous/hemizygous = male, can have male parthenogenesis but can't give females, can give grandaughters
     • Aphid parthenogenic mechanism, mother has control, loss of X during egg development, male
     • Evolution of the sex ratio: Ronald Fisher 1930
       • Insects provide insight into how distorted sex ratios arise: 1:1 = result of meiosis, no control, some insects can control, experimentally alter sex ratio
         • Local enhancement: in cooperatively breeding species favours the sex which aids most in rearing young
         • Local resource competition: philopatric species, favours the sex that disperse e,g, honey bees, (don't include sterile workers) males disperse, male bias
         • Local mate competition: female bias in viviparous insects with little need for males
         • Sex distorters: cytoplasmic agents son-killer bacterium, maternally inherited, kills sons of parasitoid wasp, PSR chromosomes, in haplodiploid arthropods, convert diploid females into haploid males by killing chromosomes
   • How do insects reproduce? similar to vertebrates, testes sperm, ovaries eggs, egg bigger, haploid, fuse, diploid zygote, sexual reproduction, parthenogenesis also possible, some alternate, some exclusive to sexual or asexual
     • Cyclical parthenogenesis and how reproductive behaviours change with conditions provide insight into the selective value of sex
     • Internal
       • Male sperm vary, spermatophores, female eggs same, spermathecal, spermathecal glands, spermathecal enzymes, gives female control over when she uses sperm and whose sperm, stimsperm releae stimulates, micropyle, fertilisation then oviposition , Dytrisia, two genital openings
     • External, ancestral
       • Females: ovipositor becomes sting, males, complex genetalia, two theories, lock and key, devalued by poor matches, sexual selection, (male-male- competition) remove other males sperm, backed up by greater complexity when females have multiple mates
     • Variations
       • Traumatic insemination, sperm injected into abdomen, diffuse to ovaries, sexual conflict, males impair female, female counteracts some of damage wit spermaleg
     • Asexual: two-fold cost of sex, (half males and lose half of genes without doubling gametes), Muller's Ratchet, benefit of asexual, get telescoping of generations
       • So why sex? shuffling of alleles and favourable mutations, evolutionary arms race e.g. parasite host co-evolution, parthenogenesis meanwhile pevents/slows adaptation and speciation

3. Insect mating systems and sexual selection - the study of has enhanced our knowledge

   • Bateman principle, males have greater vaiability in reproductive success, due to anisogamy, males number, females energy invested and size, illustrated by Bateman gradient graph, repro. success against mates, found greater variability in female direct proportionality in males
     • Consistent with Robert Triver's theory of parental investment, females limiting factor, greater variance in males therefore
   • Males take more active role + greater risks - emerge first, wait, leks, sexually dimorphic species, males have the wings or elaborate ornaments, = investment, risk to produce signal, less risky to follow,
     • When signals come at a cost = honest signal
   • Sexual selection = selection for the traits associated with repro. success, due to Anisogamy: males - number, females, energy invested, quality, tend to want as many mates as possible , females choosy, males compete two mechanisms
     • Intrasexual selection: males compete for females or the resources females need, typical of poylgynous systems
       • Before copulation: physical displays or conflict, evolved weaponry and chemical/visual/audible signals of size + strength, theoretical models suggest assess to avoid injury
         • May have alternative strategies, onthophagus, burrowing, sneak or guard and fight, sigmoidal relationship between forceps and body size, dimorphic population, threshold based on body size determines strategy
       • After copulation:
         • Sperm competition: spermatheca: oust other sperm and protect own, complex genetalia, Damselfly penis, dual function, horn and backward hairs, long copulation, Drosophila and toxic sperm inceases paternity certainty, cost to female
           • Conflict of interest often has cost, often to female, toxic sperm reduces life span
         • Mate guarding, male plugs in hees, kills male, counter productive, attracts other males, may be to benefit females, encourage multiple mating, or can physically guard
         • Prolonged copulation
     • Intersexual competition = female choice
       • Before copulation: why do females benefit
         • Tangible: direct benefits like nuptial gifts
         • Indirect: two hypotheses: sexy sons
           • Fisherian hypothesis: sexy sons, sons have better success, gene for preference and gene for trait become linked, runaway selection, positive feedback, extreme ornamentation, Evidence for hypothesis in stalk eyed flies exp.
             • Can fit in with honest signals Zahavi's handicap principle, extreme ornaments or genes expressed at a cost to male can only be expressed by high quality males, = honest signal
               • Evidence for ornaments being honest signals in experiment
           • Good genes hypothesis: no tangible benefis good genes, fitter, more repro. success in sons,
       • Cryptic female choice: use of male ejaculates in spermatheca, female choice and killing of sperm? dimorphic sperm would suggest so, eusperm, fertilise, parasperm protect ? , red flour beetles and hind leg rubbing positively correlates with fertilisation
       • How does a male benefit from female choice?
         • Paternal investment or ejaculation protection (favoured)

4. Eusociality

   • 3 orders: Hymenoptera, Isoptera, Homoptera
     • Cooperative brood care, reproductive isolation, overlap of generations (also reproductive altruism
       • Hymenoptera, 8 origins of eusociality, endopterygotes with haplodiploidy
       • Isoptera, endopterygotes, no haplodiploidy
       • Primitive (vespid wasp) vs advanced (honey bee), advanced = more extreme, physical castes, queen uses pheromones to show dominance not fighting, queen doesn't work, colony formation is cooperative queen + some workers, perennial, larger colonies