Group selection, inclusive fitness, and ants

ants (Hymenoptera: Formicidae) 10-12,000 species; 15-25% of animal biomass worldwide all are eusocial  colonies of fertile queens & sterile workers, 3 classes of offspring: gynes workers males how is eusociality produced and maintained?

ants (Hymenoptera: Formicidae) 10-12,000 species; 15-25% of animal biomass worldwide all are eusocial  colonies of fertile queens & sterile workers, 3 classes of offspring: gynes workers males how is eusociality produced and maintained?

ants (Hymenoptera: Formicidae) 10-12,000 species; 15-25% of animal biomass worldwide all are eusocial  colonies of fertile queens & sterile workers, 3 classes of offspring: gynes workers males how is eusociality produced and maintained?

inclusive fitness, kin selection W.D. Hamilton (1964, 1972), then Trivers & Hare (1976), then Boomsma & Grafen (1990, 1991) fitness = direct reproduction + effects on others’ reproduction aiding in reproduction of others is favored if: fitness benefit to relative x relatedness > fitness cost to self

inclusive fitness, kin selection W.D. Hamilton (1964, 1972), then Trivers & Hare (1976), then Boomsma & Grafen (1990, 1991) fitness = direct reproduction + effects on others’ reproduction aiding in reproduction of others is favored if: fitness benefit to relative x relatedness > fitness cost to self

inclusive fitness, kin selection W.D. Hamilton (1964, 1972), then Trivers & Hare (1976), then Boomsma & Grafen (1990, 1991) fitness = direct reproduction + effects on others’ reproduction aiding in reproduction of others is favored if: fitness benefit to relative x relatedness > fitness cost to self

ants: haplodiploidy

haplodiploidy due to haplodiploid reproduction, ant workers may be more closely related to a queen’s offspring than to their own this supports the evolution of eusociality however, conditions for r queen’s offspring > r own offspring are limited, and origins of eusociality aren’t tractable

haplodiploidy due to haplodiploid reproduction, ant workers may be more closely related to a queen’s offspring than to their own this supports the evolution of eusociality however, conditions for r queen’s offspring > r own offspring are limited, and origins of eusociality aren’t tractable

haplodiploidy due to haplodiploid reproduction, ant workers may be more closely related to a queen’s offspring than to their own this supports the evolution of eusociality however, conditions for r queen’s offspring > r own offspring are limited origins of eusociality aren’t tractable

haplodiploidy monogynous colonies & singly mated queens & 1:1 sex investment ratios  relatedness of workers to queen’s offspring = 0.5 if sex investment ratio = relatedness skew (1:3 males:females)  r = :3 sex investment ratio is generally found in these conditions

haplodiploidy monogynous colonies & singly mated queens & 1:1 sex investment ratios  relatedness of workers to queen’s offspring = 0.5 if sex investment ratio = relatedness skew (1:3 males:females)  r = :3 sex investment ratio is generally found in these conditions

haplodiploidy monogynous colonies & singly mated queens & 1:1 sex investment ratios  relatedness of workers to queen’s offspring = 0.5 if sex investment ratio = relatedness skew (1:3 males:females)  r = :3 sex investment ratio is generally found in these conditions

problems polygynous colonies? multiple mating of queens? < relatedness of workers to the queen’s offspring but if you can’t explain eusociality, at least explain sex ratios...

problems polygynous colonies? multiple mating of queens? < relatedness of workers to the queen’s offspring but if you can’t explain eusociality, at least explain sex ratios...

problems polygynous colonies? multiple mating of queens? < relatedness of workers to the queen’s offspring but if you can’t explain eusociality, at least explain sex ratios...

multiple mating multiple mating  overall relatedness drops; but relatedness to male offspring is unchanged more male-biased sex investment ratio

multiple mating multiple mating  overall relatedness drops; but relatedness to male offspring is unchanged more male-biased sex investment ratio

multiple mating effective mating frequency is generally low in ants facultatively polyandrous ants: predicted changes occur ( Leptothorax ) or not ( Lasius ) obligate polyandry (rare): predicted changes occur (Attini) or not ( Pogonomyrmex )

multiple mating effective mating frequency is generally low in ants facultatively polyandrous ants: predicted changes occur ( Leptothorax ) or not ( Lasius ) obligate polyandry (rare): predicted changes occur (Attini) or not ( Pogonomyrmex )

multiple mating effective mating frequency is generally low in ants facultatively polyandrous ants: predicted changes occur ( Leptothorax ) or not ( Lasius ) obligate polyandry (rare): predicted changes occur (Attini) or not ( Pogonomyrmex )

polygyny polygyny  relatedness drops related queens  relatedness asymmetry changes unrelated queens  relatedness asymmetry unchanged polygyny  greater cost of gynes?

polygyny polygyny  relatedness drops related queens  relatedness asymmetry changes unrelated queens  relatedness asymmetry unchanged polygyny  greater cost of gynes?

polygyny polygyny  relatedness drops related queens  relatedness asymmetry changes unrelated queens  relatedness asymmetry unchanged polygyny  greater cost of gynes?

polygyny gynes cost more  more male-biased sex ratio (or investment ratio) related queens  more male-biased sex investment ratio support mixed; polygyne ants generally more male-biased, but: competitive benefit from neighboring related nests ( Linepithema ) polygyny shifts sex investment ratios without relatedness asymmetry changes (e.g. Pheidole, Formica )

polygyny gynes cost more  more male-biased sex ratio (or investment ratio) related queens  more male-biased sex investment ratio support mixed; polygyne ants generally more male-biased, but: competitive benefit from neighboring related nests ( Linepithema ) polygyny shifts sex investment ratios without relatedness asymmetry changes (e.g. Pheidole, Formica )

polygyny gynes cost more  more male-biased sex ratio (or investment ratio) related queens  more male-biased sex investment ratio support mixed; polygyne ants generally more male-biased, but: competitive benefit from neighboring related nests ( Linepithema ) polygyny shifts sex investment ratios without relatedness asymmetry changes (e.g. Pheidole, Formica )

split sex ratios colonies often specialize in production of one sex Boomsma & Grafen (1990, 1991)  colonies specialize in sex to which workers are more related than average supporting evidence in some taxa, but: split sex ratios without any relatedness changes ( Solenopsis ) or in the opposite direction (e.g., Pheidole )

split sex ratios colonies often specialize in production of one sex Boomsma & Grafen (1990, 1991)  colonies specialize in sex to which workers are more related than average supporting evidence in some taxa, but: split sex ratios without any relatedness changes ( Solenopsis ) or in the opposite direction (e.g., Pheidole )

split sex ratios colonies often specialize in production of one sex Boomsma & Grafen (1990, 1991)  colonies specialize in sex to which workers are more related than average supporting evidence in some taxa, but: split sex ratios without any relatedness changes ( Solenopsis ) or in the opposite direction (e.g., Pheidole )

nepotism? polyandry and polygyny  selection for nepotism in workers nepotism is rare or absent!

nepotism? polyandry and polygyny  selection for nepotism in workers nepotism is rare or absent!

males? males generally ignored in inclusive fitness explanations male fitness increases with female-biased investment if sex-ratio arguments are correct  strong selection in males against multiple mating

males? males generally ignored in inclusive fitness explanations male fitness increases with female-biased investment if sex-ratio arguments are correct  strong selection in males against multiple mating

males? males generally ignored in inclusive fitness explanations male fitness increases with female-biased investment if sex-ratio arguments are correct  strong selection in males against multiple mating

phylogenetic inertia? can this explain tolerance of polygyny? workers may be stuck with sociality, but they are not stuck with polygyny, or even queens: queen-killing occurs ( Linepithema ), but not nepotistically! reproduction can (rarely) be coopted by workers ( Rhytidoponera )

phylogenetic inertia? can this explain tolerance of polygyny? workers may be stuck with sociality, but they are not stuck with polygyny, or even queens: queen-killing occurs ( Linepithema ), but not nepotistically! reproduction can (rarely) be coopted by workers ( Rhytidoponera )

so what’s the alternative? reviews of kin selection in Hymenoptera omit competing hypotheses! what about group selection?

so what’s the alternative? reviews of kin selection in Hymenoptera omit competing hypotheses! what about group selection?

group selection formed by analogy to natural selection: “This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection.” Darwin, Darwin does not specify the units of selection here

group selection formed by analogy to natural selection: “This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection.” Darwin, Darwin does not specify the units of selection here

group selection the between-group component of natural selection preconditions: heritable variation in fitness between groups this is probably a general property: random sampling error assortative group membership

group selection the between-group component of natural selection preconditions: heritable variation in fitness between groups this is probably a general property: random sampling error assortative group membership

group selection the between-group component of natural selection preconditions: heritable variation in fitness between groups this is probably a general property: random sampling error assortative group membership

group selection increased recent prominence; E.O. Wilson has announced the demise of kin selection need not be in conflict with individual-level selection increases with partitioning of variance between vs. within groups

group selection increased recent prominence; E.O. Wilson has announced the demise of kin selection need not be in conflict with individual-level selection increases with partitioning of variance between vs. within groups

group selection increased recent prominence; E.O. Wilson has announced the demise of kin selection need not be in conflict with individual-level selection increases with partitioning of variance between vs. within groups

what are groups? all units are groups at a lower level of analysis the question is: which is most explanatory? genes of ultimate importance, but selected through phenotype: which level of phenotype? primary unit of selection  reproduction? colonies reproduce

what are groups? all units are groups at a lower level of analysis the question is: which is most explanatory? genes of ultimate importance, but selected through phenotype: which level of phenotype? primary unit of selection  reproduction? colonies reproduce

what are groups? all units are groups at a lower level of analysis the question is: which is most explanatory? genes of ultimate importance, but selected through phenotype: which level of phenotype? primary unit of selection  reproduction? colonies reproduce

what are groups? all units are groups at a lower level of analysis the question is: which is most explanatory? genes of ultimate importance, but selected through phenotype: which level of phenotype? primary unit of selection  reproduction? colonies reproduce

group selection vs. kin selection within-group relatedness increases between-group partitioning of variance the two are compatible explanations, not strict alternatives but predictions & explanatory value differ

group selection vs. kin selection within-group relatedness increases between-group partitioning of variance the two are compatible explanations, not strict alternatives but predictions & explanatory value differ

group selection vs. kin selection within-group relatedness increases between-group partitioning of variance the two are compatible explanations, not strict alternatives but predictions & explanatory value differ

is relatedness the right metric? Solenopsis invicta, Linepithema humile, other major invasives characterized by unicoloniality: low or absent between-nest aggression, often across large areas relatedness in nests approaches 0

is relatedness the right metric? Linepithema humile : although relatedness is ~0, genetic similarity is high low relatedness may be a measurement artifact Solenopsis invicta : between-nest & between-queen cooperation determined by Gp-9 single-locus identity, and not relatedness, controls social form

is relatedness the right metric? Linepithema humile : although relatedness is ~0, genetic similarity is high low relatedness may be a measurement artifact Solenopsis invicta : between-nest & between-queen cooperation determined by Gp-9 single-locus identity, and not relatedness, controls social form

do colony characteristics determine success? Linepithema & Solenopsis : increased colony size  large competitive advantage Formica : increased colony size  exploitation of concentrated, long-term resources Pogonomyrmex: decreased relatedness  increased colony growth

do colony characteristics determine success? Linepithema & Solenopsis : increased colony size  large competitive advantage Formica : increased colony size  exploitation of concentrated, long-term resources Pogonomyrmex: decreased relatedness  increased colony growth

do colony characteristics determine success? Linepithema & Solenopsis : increased colony size  large competitive advantage Formica : increased colony size  exploitation of concentrated, long-term resources Pogonomyrmex: decreased relatedness  increased colony growth

explaining inclusive fitness gaps? absence of nepotism, tolerance of polygyny & low relatedness  more efficient colony function, better colony-level performance split sex ratios may be determined by colony-level factors: resource limitation local mate competition habitat saturation

explaining inclusive fitness gaps? absence of nepotism, tolerance of polygyny & low relatedness  more efficient colony function, better colony-level performance split sex ratios may be determined by colony-level factors: resource limitation local mate competition habitat saturation

but: the forgotten variables cost & benefit terms of Hamilton’s rule generally ignored can we accomodate everything by hiding it in those variables? yes, you can! but there is no explanatory or predictive value and it obscures explanatory integration

but: the forgotten variables cost & benefit terms of Hamilton’s rule generally ignored can we accomodate everything by hiding it in those variables? yes, you can! but there is no explanatory or predictive value and it obscures explanatory integration

but: the forgotten variables cost & benefit terms of Hamilton’s rule generally ignored can we accomodate everything by hiding it in those variables? yes, you can! but there is no explanatory or predictive value and it obscures explanatory integration

integration Pogonomyrmex genetic variation & productivity: is this analogous to heterozygote advantages? split sex ratios: aren ’ t we looking at evolution of gonochorism, one level up? do we want to reinvent the wheel for group-level explanations?

integration Pogonomyrmex genetic variation & productivity: is this analogous to heterozygote advantages? split sex ratios: aren ’ t we looking at evolution of gonochorism, one level up? do we want to reinvent the wheel for group-level explanations?

integration Pogonomyrmex genetic variation & productivity: is this analogous to heterozygote advantages? split sex ratios: aren ’ t we looking at evolution of gonochorism, one level up? do we want to reinvent the wheel for group-level explanations?

conclusions origins of eusociality not tractable in ants kin selection predictions for sex ratio hold for monogyny + monandry, fail in other cases kin selection explanations neglect male fitness; predict nepotism; rely on constraints

conclusions origins of eusociality not tractable in ants kin selection predictions for sex ratio hold for monogyny + monandry, fail in other cases kin selection explanations neglect male fitness; predict nepotism; rely on constraints

conclusions origins of eusociality not tractable in ants kin selection predictions for sex ratio hold for monogyny + monandry, fail in other cases kin selection explanations neglect male fitness; predict nepotism; rely on constraints

conclusions group selection (or multilevel selection) includes kin selection explanations accounts for variance independent of relatedness aids explanation of colony functionality, fosters integration of theory across levels

conclusions group selection (or multilevel selection) includes kin selection explanations accounts for variance independent of relatedness aids explanation of colony functionality, fosters integration of theory across levels

conclusions group selection (or multilevel selection) includes kin selection explanations accounts for variance independent of relatedness aids explanation of colony functionality, fosters integration of theory across levels