1) Altruism in Social Insects

Question 1

What is natural selection

Answer 1

Natural selection is the differential survival and reproduction of individuals due to differences in phenotype

Question 2

What is altruism

Answer 2

Behaviour of an animal that benefits another at its own expense. Acting to increase another individuals lifetime number of offspring at a cost to ones own survival and reproduction

Question 3

what is the difference between direct and indirect fitness?

Answer 3

Direct fitness- the number of offspring the individual procreates
Indirect fitness- the number of offspring produced by the genetic relatives of the individual

Question 4

when is altruism likely to occur and why

Answer 4

1) genetic predispositions- individuals may aid close relatives (such as siblings) thereby making a genetic profit in terms of indirect fitness. Individuals must leave as much genetic material behind as possible even indirectly

2) Ecological constraints- habitat saturation, resource constraints (food, breeding territory), lack of potential mates. ie the option of becoming a parent is unavailable. research woodpecker example. helpers may also increase their own chance of survival or future reproduction by staying at home

Question 5

What is kin selection

Answer 5

kin selection, a type of natural selection that considers the role relatives play when evaluating the genetic fitness of a given individual. It is based on the concept of inclusive fitness, which is made up of individual survival and reproduction (direct fitness) and any impact that an individual has on the survival and reproduction of relatives (indirect fitness). Kin selection occurs when an animal engages in self-sacrificial behaviour that benefits the genetic fitness of its relatives. The theory of kin selection is one of the foundations of the modern study of social behaviour. British evolutionary biologist W.D. Hamilton first proposed the theory in 1963 and noted that it plays a role in the evolution of altruism, cooperation, and sociality.
Behaviour which appears to be altruistic at the phenotypic level is actually genetically selfish. Natural selection that considers the role relatives play when evaluating the genetic fitness of a given individual. It is based on the concept of inclusive fitness which is made up of individual survival and reproduction (direct fitness) and any impact that an individual has on the survival and reproduction of relatives (indirect fitness). Kin selection occurs when an animal engages in self-sacrificial behaviour that benefits the genetic fitness of its relatives. Key point- Parent-child relationship - 50% relatedness. full siblings- 50% related. ie a sister should care for her sister the same way she would her daughter as they share the same amount of genetic material. thus genetically selfish (see more in Gareth’s lecture

Question 6

So if altruism is arguably more favourable, why is care for offspring favoured over care of siblings?

Answer 6

if we view altruism and helping purely from the viewpoint of making a profit for selfish gene, arguments for parental care should apply in equal force to caring for siblings. So why is parental care favoured?
competition- your own young are less likely to compete for food with you. your siblings will compete. siblings may not be recognised. easier to recognise young than siblings.

Question 7

Discuss eusociality in social insects

Answer 7

Eusociality (from Greek εὖ eu “good” and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generations within a colony of adults, and a division of labor into reproductive and non-reproductive groups. The division of labor creates specialized behavioral groups within an animal society which are sometimes referred to as ‘castes’. Eusociality is distinguished from all other social systems because individuals of at least one caste usually lose the ability to perform at least one behavior characteristic of individuals in another caste. Eusocial colonies can be viewed as superorganisms.

Eusociality exists in certain insects, crustaceans, and mammals. It is mostly observed and studied in the Hymenoptera (ants, bees, and wasps) and in Blattodea (termites). A colony has caste differences: queens and reproductive males take the roles of the sole reproducers, while soldiers and workers work together to create a living situation favorable for the brood. In addition to Hymenoptera and Blattodea, there are two known eusocial vertebrates among rodents: the naked mole-rat and the Damaraland mole-rat. Some shrimp, such as Synalpheus regalis, are also eusocial. E. O. Wilson and others[1][2] have claimed that humans have evolved a weak form of eusociality, but these arguments have been disputed.[3]

the evolution os eusociality in social insects sich as termites, ants and some bees and wasps have been regarded as a major evolutionary transition (MET). The fitness of the lower- level units is completely transferred to the higher level. Individuals can only increase their fitness by increasing the reproductive success of the colony. 12000 species of social insects which is the total population of all birds and mammals

Question 8

Discuss criteria for eusociality

Answer 8

social behaviour involves cooperation between individuals of the same species. The degree of that cooperation defines the type of sociality that species demonstrate. workers are morphologically distinct from queens. In many species the differences are behavioural/physiological not morphological.

Question 9

What are the three definitions of eusociality

Answer 9

1) cooperative brood care
2) overlap of generations
3) reproductive division of labour

Question 10

DIscuss what insects are eusocial

Answer 10

Orders
Isoptera (termites)
Hemiptera (true bugs)
Thysanoptera
Coleoptera
Hymenoptera- ants: all species, except a few highly derived. around 14000
- bees: only 300-400 of 4000 species are eusocial
- wasps: most are not social, around 900 species are eusocial

Question 11

How can eusocial be separated from other social systems?

Answer 11

individuals of at least one caste usually lose the ability to perform at least one behavior characteristic of individuals in another caste. Eusocial colonies can be viewed as superorganisms.

Question 12

what is the difference between eusocial and subsocial

Answer 12

sub- below
1) aggregate or
2) have division of labour
3) care for eggs or young after egg laying

eu-true
1) cooperative brood care (daycare)
overlapping generations
reproductive division of labour (castes)

Question 13

list species as sub or eusocial

Answer 13

subsocial- cockroaches, crickets, earwigs, beetles, certain species of wasps
eusocial- termites, bees, wasps, ants

Question 14

list and define all examples of social systems

Answer 14

1) solitary- showing non of the three traits of sociality
2) subsocial- adults show some care of young
3) communal- ,members of the same generation use the same nest without cooperative brood care
4) quasisocial- members of the same generation use the same nest with cooperative brood care
5) semicosial- quasisocial, plus reproductive division of labour
6) eusocial- cooperative brood care, overlapping generations, reproductive division of labour

Question 15

whats the selective advantage of eusociality

Answer 15

improved foraging efficiency, enhanced defence against predators and increased reproductive success. resource ability. protection numbers.
disadvantages- disease. lots of individuals in large groups there is potential for disease spread.

Question 16

Discuss eusocial castes

Answer 16

Morphologically and behaviourally different individuals within a colony. colonies often populated by individuals specialized to perform different tasks.
examples-
Nasutitermes Exitosus termite- soldier termite: head shape of water pistol in the soldiers- will shoot stick y droplets out at the intruder.
Componutus trucates termite- soldier ant, head shaped like a plug which will be inserted into the entry to the nest to prevent entry (doorkeeper ant)
Bombus impatiens- bumble bees. queen worker and drone. variety of f workers in different sizes.

Question 17

Discuss evolution of eusociality

Answer 17

Two hypothesises- families at some and shared nest
- sterile castes originated as daughters staying at home to help mothers(subsocial route to eusociality)
originated from groups of reproductive nesting together in which one female dominated the rest (parasocial route to eusociality)

ecological constraints- two main ecological factors are likely to have favoured staying at home
1) defence of eggs and larvae against parasites and predators.
2) nest building

genetic predisposition- recipients of aid are close relatives of the altruist

Question 18

what is haplodiploidy

Answer 18

Haplodiploidy- males develop from unfertilized eggs and are haploid
females develop from normally fertilized eggs and are diploid. Female workers are 75% related to each other
note- females(dilopid) meisois occurs. Male (haploid) mitosis occurs. males get all chromosomes from mother. females have 32, males have 16. hapolid males form gametes without meisosis- each sperm is genetically identical. Each daughter receives an identical set of genes to make up half her dilpod genome. the probability of sharing a gene via the father is 1. other half of her genome comes from her diploid mother so she has a 50% chance of sharing one of her mothers genes with a sister. sisters probability of sharing a gene via the mother is 0.5- meisosis.
female workers- half of their genome is always identical the other half has a 50% chance of being shared. full sisters are more closely related to one another than are parents and offspring in a normal diploid species. a female worker can make a greater genetic profit by rearing a reproductive sister than she could if she suddenly became fertile and produced a daughter.

Question 19

discuss haplodiploidy and altruism

Answer 19

eusociality and altruism are rare. even in mammals that reproduce clonally
haplodiploidy is common in hymenoptera but eusociality is rare
termites- eusocial and have sterile castes but not hapkodiploid
haplodiploidy in the hyenoptera may predispose them to become eusocial, but it does not cause eusociality to evolve.
calculations of relatedness hold only if the colony is formed by a single queen who has mated once

Question 20

discuss sex ratios

Answer 20

trivers and hare (1976)
- the stable ratio from the queens viewpoint is 1:1. queens are equally related to daughters and sons.
- however, the stable ratio from the workers viewpoint is 3:1 females:males. workers will be three times more closely related to sisters than to brothers.
trivers and hare 1976 argued that workers should usually control sex allocation because they typically outnumber queens and rear the brood.
in agreement with the resulting prediction of the trivers-hare model, sex investment with the resulting prediction oft he trivers- hare model, sex investment ratios in many species of social hymenoptera are female biased

Question 21

Discuss maternal manipulation, mutualism and reciprocal altruism

Answer 21

maternal manipulation- it isnt altruism, it is forced by mother. manipulation of feeding-> reproductive development. selfish maternal behaviour is the primary agent selecting for eusociality

mutualism
- mutualism defence of brood creates individual selective advantage to cooperation
inclusive fitness and kin selection can maintain cooperation and push towards altruism

reciprocal altruism
-cost to the altruist is offset by likelihood of a return benefit. example- female vampire bats will share food. unregulated female vampire bats will share food. unrelated females are more likely to share food with those that had recently shared with them.