Lecture 7: Ecology and Evolution

Reading:  None.

Inclusive Fitness Effects

Individuals carrying genes identical by descent are relatives (family members).

Genetic relationships can be expressed as the coefficient of relationship (r), the proportion of genes identical by descent.

Given sexually reproducing, diploid organisms:

Altruism: Behavior benefiting another individual while being detrimental to the individual providing the benefits. Benefits and detriments are defined in terms of survival and reproduction.

"Altruism" is defined in much the same way that Darwin’s Challenge is framed. This is behavior that we predict cannot be produced by natural selection.

Aiding relatives is an alternative means of individual reproduction, which depends on:

• The magnitude of r. The greater the value of r, the more
  likely two individuals have genes identical by descent in
  common.
• Magnitude of benefit to aid receiver (includes reciprocity).
• Magnitude of cost to aid giver (depends on alternative
  activities).
• Magnitude of benefit to aid giver from sources other than
  the aid receiver.

Natural selection molds phenotypes. Behavioral traits may appear selfish or altruistic, but all are ultimately selfish in an evolutionary sense.

Can altruism evolve by means of natural selection?

Imagine a cleaner fish species in which individuals get no benefits from cleaning parasites from other fish species, but cleaners did sustain some costs. If there were variation in the cleaner fish population so some individuals were cleaners and others were non-cleaners, and the variation was heritable, which behavioral trait would be most successful in leaving descendents?

If the process of evolution by natural selection applies to all organisms, then it must apply to human too. A vulgar theory? Does it apply to humans?

Does altruism occur in human behavior?

	adoption
	life saving
	anonymous gifts

Behaviors that appear to make no sense today may have clearly been biologically selfish in their original context. Humans are not living in the environments in which we evolved, physical or social. Context (environment) is essential for understanding the evolution and maintenance of phenotypic traits.

An evolutionary view of life provides a framework for interpreting ultimate function, the origin of phenotypes, structure and function. The theory of evolution by natural selection enables us to interpret how phenotypes were molded to their present state, but this theory does not indicate what should be.

Speciation

Species Definition: Biological Species Concept

A species is a population (or group of populations) within which there is interbreeding in nature, but this group is reproductively (genetically) isolated from other such populations or groups.

Species are natural-biological groupings.

In practice, groupings are based on easily identified aspects of phenotypes. The biological species concept is limited to sexually reproducing organisms. A given species identification is not precise because our knowledge about interbreeding and gene flow between groups is not perfect. Populations are not continuous. Within populations there can be spatial isolation (separation in space) or temporal isolation (separation in time).

Species Formation

	Reproductive isolation = barrier to gene flow
	One population splits into two populations

Forms of Isolation

Allopatric: geographic or allopatric speciation, physical isolation

Changes occur in isolation in response to local conditions and chance events. The form of physical isolation necessary for reproductive isolation depends on the particular organism involved.

Parapatric: parapatric speciation

Reproductive isolation among members of a continuous population without geographic barriers. Isolation involves environmental discontinuity, such as a soil type change for plant species or host plant change in an herbivore.

Sympatric: sympatric speciation

Speciation with overlapping distributions among the two populations that are becoming isolated. Isolation may be spatial or temporal.

	Polyploidy formation in plants (rare in animals)         autopolyploidy - within a species         alloploidy - between species
	Host races         insects returning to natal plant species to reproduce
	Reproductive habitat races         fishes and amphibians that return to the site habitat         to reproduce or exhibit fidelity to "birth" site for         reproduction

What happens in isolation?

Isolation alone does not make organisms different from each other:

	reproductive behavior changes
	temporal or spatial reproductive changes
	physiological changes

Small differences can be magnified at recontact between groups if hybrids are less viable than either "pure" type. This phenomenon is termed character displacement (to be considered in detail in section on competition). Even when phenotypic differences are great, genetic differences can be very small.

Higher level systematics are groupings of species based on phenotypes (similarities and differences, shared characteristics) that are hoped to reflect evolutionary descent relationships:

	Species grouped in a Genus
	Genera grouped in a Family
	Families grouped in an Order
	Orders grouped in a Class
	Classes grouped in a Phylum
	Phyla grouped in a Kingdom

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