Chap 5 BEHAVIOR

Evolution by natural selection has become the great unifying concept of biology.

BEHAVIOR Chap 5 Adaptiveness Evolutionarily Stable StrategiesCultural TransmissionGenes & BehaviorKin Selection & Inclusive Fitness

Adaptiveness of Behavior

• Natural Selection equally operates on behavioral traits, no matter how trivial• The male mole cricket• The wing structure, singing and

burrow-digging behavior are all precisely co-adapted to produce an efficient sound aimed at female.

Efficient sound production favored by natural selection

• The Black-headed Gull removing the empty eggshells, • less vulnerable to crows and herring

gulls.

Kittiwake gull do nothave to throw away the Egg shells,

with nest on the cliff ledges

How effective the natural selection can be in the shaping of behavior.

It often result not in the best but in the best compromise, because

one single aspect of behavior can rarely evolve in isolation.

not the best but the BEST COMPROMISE• displays or loud songs• attract their mates, are also likely

to • attract the a predator. • the croaking frog attracting

mate….. frog-eating-bat.

• Evolutionarily Stable Strategies(ESS),simply a specific action of an animal, as removing egg shell. • female wasps which uses burrows

dug by other wasps; the success of the strategy depends on whether few or many digger wasps present. frequency dependent.

ESS benefits depends on what other animals around are doing, • Applied to aggression , the best

strategy (e.g attack or retreat) is very dependent on what strategy an opponent takes up.

Cultural Transmission of Behavior

• a behavioral trait may be horizontally propagated, without any genetic changes involved ______ the cultural evolution.

• E.g : the human languages and culture• In other primates, Macaques washing

potatoes.• Chimpanzees fish for termites• Opening of milk bottles by blue tits in UK

• The chick’s ability to learn song

depends on both biological and social cues.

Maintenance of the song dialect in many birds e.g White Crowned Sparrow.

• The chick’s ability to learn song depends on both biological and

social cues. • A. If exposed to the songs of many species while growing up, the

chick invariably picks out and learns the correct song. • B. If isolated during the song-learning phase, the chick produces

only a rough outline of the normal song.

• C. If deafened at an early age, the chick’s song is

entirely abnormal. • D. A chick that is socially (but not acoustically) isolated

from its own species but in contact with the adult of another species learns its tutor’s song.

• Alaram Calls development , in black bird• Chicks see the plastic bucket while

the adults are shown the stuffed owl

Genes and Behavior• Genes are the products of evolution. Evolution is

about changes in gene frequency “the genes making the more fit”

• Easy to contemplate genes for physical characters, but GENES FOR BEHAVIORAL TRAITS!

• Behavior: Interaction of nerves, muscles, sense organs, hormones etc.

• Many difficulties in studying behavioral genetics(especially in humans)

Drosophila• Bar eye, reduces the number of facets in

compound eye.• The white eye, reduces pigment

O-> difficulty in locating O+• Vestigial or dumpy Wings, O-> unable to vibrate wings

All these genes affect the courtship behavior

DrosophilaMosaic Flies(Hotta 1976) are genetically

different in different parts of their body. E.g. Gynandromorphs: some cells are O-> some O+.

Gynandromorphs: some cells are O-> some O+.

DrosophilaGynandromorphs:

The male pulse vibrating depends on the presence of males cells in mesothoracic ganglia

We could not expect such results in vertebrates, where sexual behavior develops as a result of hormones, secreted by the gonads, that affect the whole body

We could not expect such results in vertebrates, where sexual behavior develops as a result of hormones, secreted by the gonads, that affect the whole body

We could not expect such results in vertebrates, where sexual behavior develops as a result of hormones, secreted by the gonads, that affect the whole body

• An examples of naturally occurring behavior showing a classical Mendelian pattern Gwadz's (1970) .

• The females of different populations of mosquitoes become sexually receptive at different times after emergence. The females of one strain GP receptive 38h. In another strain TEX takes much longer 120. Hybrids between the two strains TEX/GP) , with a mean of about 54 h, but with a slope like GP strain.

• When the F1 hybrids were backcrossed to the GP and TEX parental strains, the results were compatible with the idea that early receptivity was due to a single, autosomal, semidominant gene.

• GP[38 h] X TEX [120 h]• GG TT

• F1 GT[56 h]

• GT X GG

Gametes G T

G GG (38 h) GT(56 h)

G GG(38h) GT(56 h)

Classic Mendelion Results are rare in Behavior Genetics.

Behavioral traits affected by more than one gene, or large number of genes may interact to produce a certain behavior, which in most of the cases is not an all or non phenomenon.

Mice can not be classified as aggressive and non-aggressive____________Continous Variation need quantitative genetics.

Migratory Restlessness in Different populations of Black Cap

• Corelation between how far they have to migrate and the intenisty of migratory restlessness at the time of migration

• Those who had to go far-away___More restless

Canary Islands

Finland

AFRICA

Crosses between birds from different populations resulted in hybrids with intermediate degrees of restlessness

• Two lovebirds of the Genus Agapornis • The peach-faced tuck the nest material in to their

rump, while Fischer’s lovebird carry the strips singly in their bill

• When crossed• The hybrid for some time not capable of building the

nest because they were attempting some sort of compromise between the two.

• After months of practice, successful only in 41 % trials

• Two years later 100 % sucessful, but before carrying a strip in their bill they would make a brief turning movement of the head( a reminiscent of tucking).

Hybrids were sterile so the F2 or F3 could

not be known.

The Rate of Mating in Pairs of Drosophila

Genetic Lines relevant to Behavior

can be selected

KIN SELECTION AND INCLUSIVE FITNESS

Darwin was aware of altruistic social behavior in animals, and of how this phenomenon challenged his theory of natural selection.

Eusociality in Hymenoptera

2n O+ Workers and Queenn O-> Drones

• bees colony, worker bees are responsible for collecting food, defending the colony, and caring for the nest and the young, but they are sterile and create no offspring.

• Scientists now recognize that among social insects, such as bees, wasps, and ants, the sterile workers are actually more closely related genetically to one another and to their fertile sisters, the queens, than brothers and sisters are among other organisms.

• Samuel Butler, A chicken is an egg’s way of producing another egg’• An animal is a gene way of producing

more copies of that gene• Some people uneasy with A gene-

centered view of evolution / existence. • Consider Parental Care

• Success in evolutionary terms means leaving offspring that themselves reproduce, but the 'success' of an individual is short-lived and ephemeral. In sexually reproducing species, an individual does not survive for more than one generation. But the genes are passed on to the future generations>>>>

Inclusive fitness• Hamilton invented the idea of inclusive

fitness. Fitness can be divided into two components: • Direct fitness results from personal

reproduction• Indirect fitness results from additional

reproduction by relatives, that is made possible by an individual’s actions.

Hamilton’s Rule• The rule generalized the circumstances in

which relative-helping of various sorts would evolve into the equation:

Br - c > 0, B is the benefit to the relative/actor and r is the coefficient of relatedness c the cost to the relative-helping genotype.

r b - c > 0, calculating values for r, b and c.

• r does not cause problem. r is the probability that the homologous alleles in two individuals are identical by descent.

• From basic genetics• Full Siblings, and Parents & Offspring have a 50 per

cent chance of sharing a given rare gene• (r = 0.5); • Nieces and Nephews have a 25 per cent chance of

sharing with an uncle or an aunt• (r = 0.25) and so on.

Calculating r• To calculate r one should trace each path

between the two individuals and count the number of steps needed. Then for this path r = 0.5 (number of steps)

• Thus, if two steps r for this path = 0.5 (2) = 0.25.

• To calculate final value of r one adds together the r values calculated from each path.

• It is not just the degree of relatedness that matters, but the number of relatives that can be helped.

• Haldane, “ I am prepared to lay down my life on behalf of four grandchildren or eighth first cousins!”

r b - c > 0, values b and c More Problematic

• How to measure the effect of help. If we observe one animal helping another torear its yourn, how do we know that the parent wouldn’t have been just as scessful without the help?

• Ando how do we know whtat the cost to the helper was in terms of the offspring it wold have had if it hadn’t been helping someone else?

• The mythical offspring

r b - c > 0, values b and c, Some Practical Examples

• Hamilton on Isoptera(termites) and Hymenoptera(ants, bees, wasps)

• With Extreme Altruistic Behavior.

The 0.75 relatedness among Hymenoptera Sisters

How to Explain the sociality of Termites

1 0 0 0, 0 0 0 s Offspring

Naked Mole-rats

• Naked mole-rats are highly unusual mammals.

• They are nearly hairless and ectothermic. They are eusocial and, like termites, can digest cellulose with the help of bacteria in their gut.

Fig 51.33

Naked Mole Rats

Naked Mole-rats

• The behavior of naked mole-rats is similar to that of colonial insects.

• There is a single reproductive female (queen) and 1-3 reproductive males. The remaining individuals act as workers. They dig tunnels to find food, defend the tunnel system from other mole-rats, and tend the young.

Naked Mole-rats

• Leading hypothesis for why naked mole-rats are eusocial is inbreeding.

• Average coefficient of relatedness is 0.81 and about 85% of matings are between parents and offspring or between full siblings.

Naked Mole-rats

• Despite high level of relatedness conflicts still occur because reproductive interests of workers and reproductives are not identical.

Naked Mole-rats

• Queens maintain control through physical dominance.

• Queen aggressively shoves workers who do not work hard enough and shoves are mainly directly towards less closely related individuals.

• Workers double their work rate after being shoved.

Naked Mole-rats

• In addition to inbreeding, ecological factors such as severely limited breeding opportunities and group defense appear to contribute to eusociality in naked mole-rats.

“We are survival machines—robot vehicles blindly

programmed to preserve the selfish molecules known as

genes”

You can study other examples in the Chapter 5 reading given to youOther examples are

from Birds, Jackals etc