Recognition

I. Definition of recognition:

Discrimination and identification of a target individual or group [or habitat] from among a field of similar nontarget individuals or groups [or habitats]

II. Types of recognition and possible benefits of discrimination

A. Species (direct benefits)

B. Prey, predators, parasites (direct benefits)

C. Habitat (direct benefits)

D. Mate (benefits for reproduction)

1. sex recognition
2. mate quality

E. Individual (direct benefits via reciprocity, cooperation, social integration)

F. Kin (indirect benefits via kin selection, nepotism and direct benefits via inbreeding avoidance)

G. Group membership (direct benefits of group membership)

H. Self versus nonself (immunity)

III. Process of recognition

1. the sender provides information about its identity in the form of a signal

2. the receiver perceives the signal against background noise

3. the receiver compares the signal to a model or template

4. the receiver decides whether sender is / is not the target

5. the receiver takes some action based on its decision

III. Central problem of recognition is discrimination of target from nontarget

1. Example of mother bat deciding whether to nurse a calling infant bat in a large creche -- a dichotomous recognition task

A. X axis describes the range of variation of the difference between the template of the female bat and the actual phenotypes expressed by infant bats for both target and nontarget classes (e.g. difference between a female bat's template of what her offspring sounds like and the sounds that different classes of offspring in creche make). Note that target and nontarget classes can have overlapping distributions.

B. If a mother bat has single cut-off in deciding to accept versus reject a calling offspring, then then two types of error

a. Misses: missing giving aid to own offspring
b. False alarms: gives aid to nonrelated offspring
c. Moving cutoff can decrease one type of error but will increase other
d. Thus recognition is rarely perfect, and cheating is possible and may even be tolerated

2. How can this sort of relationship be changed through evolution?

A. Evolution of target either to make more distinct signals to minimize misses or to make less distinct signals and take advantage of other mothers' false alarms

B. Evolution of receiver for increased discrimination ability -- e.g. take more time, use more cues

3. In general, the more classes to be discriminated, the more complex the task involving more memory and demanding more complex signals.

4. Most complex signals are required for individual recognition -- e.g. frequency modulated signals with harmonic structure

IV. Mechanisms of recognition: three main classes, but many systems involve multiple mechanisms

A. Spatial location -- recognition decision is based on proximity to a location

Examples: Brood parasitism in cowbirds, cuckoos, ducks -- parsitized birds raise chicks as their own

Benefits: a simple decision rule, low decision costs, low cost to develop, no selection on sender to develop special signal

Costs: easy to subvert by cheaters

B. Familiarity -- recognition is based on past experience followed by memorization of specific characteristics; recognition decision is based on degree of matching to this template

Example: Naked mole rats live in xenophobic colonies and treat unfamiliar animals, kin or nonkin, with equal hostility; familiar or resident animals who are removed from colony and reintroduced are accepted back into colony

Example: Belding's ground squirrels -- use multiple recognition cues

Females chase close kin trespassers less often than distant kin or nonkin trespassers suggesting that some kin recognition occurs

Up until age 25 days, pups can be cross fostered suggesting that spatial location is an important recognition cue

Sibs and nonsibs reared together treated with less aggression than sibs and nonsibs reared apart (left graph) suggesting familiarity is important

For female-female pairs, sibs reared apart treated with less aggression than nonsibs reared apart (right graph) suggesting yet another cue, not based on familiarity, is used for kin recognition

Benefits: harder to cheat on that recognition based on spatial cues, allows greater discriminability, can be used for individual, kin, or group level recognition

Costs: requires a variable signal, more memory

C. Phenotype matching -- functions to identify genetic similarity among close kin

Uses a variable phenotype that is highly correlated to genetic similarity. The receiver compares sender's phenotype to a know referent, usually either a familiar relative or self

Example: Male beavers will scent mark on shores of bodies of water in their territories and investigate the scent marks of other male beavers. They respond less strongly to scent marks of siblings even though they have never come into direct contact with those siblings (who are thus unfamiliar animals). This is true of scent marks based on anogenital secretions (AGS) but not secretions from the castoreum. Interestingly, mates of male beavers respond less strongly to the scent marks of their mates siblings than to other males.

Example: MHC -- many recent studies support idea that MHC is used in kin recognition is a variety of animal taxa

1.The major histocompatability complex is a set of hypervariable genetic loci (many alleles) the products of which are cell surface protiens that seem to play a major role in disease resistance, parasite detection, and recognition of self versus nonself

2. Because of high allelic diversity, most individuals are heterozygotes and only kin are likely to chare alleles

Experiments for MHC-based recognition

A) Create inbred mice that differed only at MHC locus
B) Allowed to associate in semi-natural enclosures in barns
C) Females preferred to mate with males whose MHC alleles differed from theirs
D) Females preferred to associate with MHC-similar males
E) Similar effects in shown in humans where females asked to rank the "pleasantness" of smell of T-shirts worn by MHC-similar and MHC-different males

Benefits: mate with MHC-different to avoid inbreeding and associate with MHC-similar for nepotism, kin selection, allows for recognition of close kin, very hard to subvert

Costs: may be difficult to evolve or to maintain suffient polymorphism in population

References:

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