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Comprehensive Essay on “Cooperation in Animals”

January 16, 2019 0 Comment

Ants, bees and wasps exhibit “haplodiploidy”. Males are haploid and develop from unfertilized eggs. Females are diploid and develop in normal fashion from fertilized eggs. All sperms from one male are therefore identical. When queen bee fertilizes eggs with this sperm, all resulting daughters received same paternal chromosomes and has half their genes in common.

They share, on average all the genes inherited from their common mother and so their degree of relatedness, r = 0.75 (0.5 from j father plus 0.5 0.5 = 0.25 from mother). Thus, although workers are sterile, many genes that they share with young queens (which are also their sisters) will be passed on to next generation.

Sterile workers benefit, not because they help other workers which are closely related to them but are a reproductive dead-end, but because they care for small number of their sisters which will develop into young queens.

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In gene terms, it is more advantageous for female Hymenopterans to stay and help to rear her closely related reproductive sisters than to leave and attempt to rear less closely related daughters of her own.

Haplodiploidy appears to predispose Hymenoptera to high degree of sociality. A similar degree of sociality is also shown by termites. They have an ordinary diploid mating system. Sterile workers of both sexes’ have degree relatedness to young reproductive’s of only 0.5. King and queen termites are long lived and monogamous.

A queen laid up to 36000 eggs a day and in some species lives for have literally millions of offspring in there, lifetime, vast majority of which will never reproduce at all. Understanding why so many termite workers should be sterile, we have to follow three variability Hamilton’s equations.

A high predisposes towards helping because it increases effective benefit but even a relatively low value of r would lead to helping, if benefits were high enough and costs low enough.

Cost to each worker of being sterile is loss of these offspring, it would have had, if it had not been helping colony. Given that a pair of termites on their own would probably not survive, let alone reproduce even modestly, costs of helping must also be small (no hope of reproducing means no cost to losing it).

Monogamy in termite breeding system means that workers are guaranteed a long series of full brothers and sisters to take care of. Since their own parents offer no care to them, without workers young termites would die.

Workers therefore, make a substantial difference to survival chances of close relatives, even though benefit, b, accruing to each worker is only a fraction (because it is shared with other workers which have helped) of output of each reproductive. Nevertheless, it appears that benefits of helping are significant, costs low and r at least as high as between diploid parents and offspring.

Termites often live in deserts or in very dry regions and can only do so, because mounds, built by collective labours of millions of workers, enable them to create their own microenvironment. A single pair of termites, removed from this specialized microenvironment, would stand no chance, and this fact effectively reduces costs and increases benefits of helping the royal pair in home colony. (Manning and Dawkin, 2002).

Despite the popular conception of sharks as “long killers”, many species feed in groups. Coles reported astonishingly coordinated manner in which a group of hundred or more sand tigers of Cape Lookout, North Carolina, systematically surrounded school of blue fish and herded them into shallow water.

Similar instances have found at Seal rocks, New South Wales from where a diver reported a pack of sand tigers, known locally as Grey Nurse Shark, herding a small shoal of juvenile yellow tail king fish (Seriola lalandi) by whipping their tails to generate sharp under water pressure waves, which sound very like reports of a shotgun.

Cooperative herding behavior by using of bottom topography to strand schooling fishes has often observed in bottlenose dolphins (Trtisiops truncates), feeding on mullet at several coastal wetland location of southeastern United States.

Co-operative Hunting in Wild Dogs:

A lone wild dog can successfully kill a medium sized ungulate such as an impala, but group hunting increase overall hunting success and allow the group to capture larger prey. Hunting success increased from 42% for a group of three adults to 67% for a pack with 20 adults.

Mass of prey killed also increased as pack size increased (21kg for pack of three dogs to 68 kg for a pack of 20 dogs) while chase distance decreased for larger packs. An important reason for co-operative hunting is defense from Kleptoparsitism.

A lone wild dog would never be able to defend its kill from a pack of scavenging hyenas but a pack of wild dogs can often chase off a group of hyenas. A small pack may have lower hunting success and may often lose their kill to kleptoparasites.

But usually each dog has more to eat at a successful kill. Similarly, a large pack may have greater hunting success and may rarely lose kills to kleptoparasites, but each dog will get less food at a given kill. Benefits and costs of cooperative hunting change with differences in pack size, age and experience of pack members and habitat but in end, cooperative hunting is a crucial element of wild dog behaviour.

Co-operative Breeding in Birds:

The term co-operative breeding describe situations in which adult individuals (helpers), in addition to genetic parents regularly aid in rearing of young. This has been reported in at least 3.2% of extant bird species (308 co-operatively breeding species, out of a total 9672 species). Helpers are reproductively capable younger individuals that after attaining of maturation delay dispersal remain with and aid their parents in rearing of a later brood.

These types of helpers are actually termed as primary helpers. There are second types of helpers which after attaining maturity disperse from their natal family, then join and aid distantly related/unrelated breeders. These are called secondary helpers.

Simplest way to assess the importance of helpers on success of individual reproductive attempts is to compare production of young from nests tended by breeding parents alone with that from nests tended by three or more adults.

Many simple co-relational analyses of this sort show a seemingly positive influence of helpers. In white fronted beef eaters, linear trend of increasing fledging success with increasing helper number was maintained, when environmental conditions as well as age and experience of breeding pair, were treated as covariates.

Action of helpers has a major impact in increasing fledging success in this species. It appears that helpers have a moderate effecting enhancing breeding success in large number of species and a strong effect in few. There are number of species however, in which no influence of helpers on success of individual’s reproduction attempts has been found.

No one really seems to know why individuals should cooperate. Some economists and scientists have argued that co-operation is not a rational or logical behaviour for individuals species since energy or other resources must be expended in effort, with no direct benefit to individuals. Fehr and Simon (2002) rejected such thinking.

They argue that logic applies not just to ends but also to means during economic decision- making and commented that “there is nothing irrational in being altruistic”. General conceptual framework discussed is largely based on avian and mammalian studies. Works on co-operation among animals belonging to other species taxa are also required (Aich et al., 2006).

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