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Cultural transmission of tool use in bottlenose dolphins

Cultural transmission of tool use in bottlenose dolphins. Krutzen et al. Anthony Jensen Joseph Byers Katherine Mahoney. Source of ongoing debate Consensus towards continuity A behavioral trait is considered to vary culturally if Acquired through social learning

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Cultural transmission of tool use in bottlenose dolphins

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  1. Cultural transmission of tool use in bottlenose dolphins Krutzen et al. Anthony Jensen Joseph Byers Katherine Mahoney

  2. Source of ongoing debate • Consensus towards continuity • A behavioral trait is considered to vary culturally if • Acquired through social learning • Transmitted within/between generations Culture in the animal world

  3. Evidence for the existence of culture • Primate communities • Chimpanzees, orangutans • Geographic variation associated with behavioral variation (tool use, foraging…) • Evidence for observational learning Culture in the animal world

  4. Sponging Behavior in the Bottlenose Dolphin

  5. Longitudinal study since 1984 • Shark Bay, Western Australia • Numerous and diverse foraging tactics within pop. • Sponging – single instance of tool use • Female-biased behavior • 15 of 141 known mothers (1 male!) • 7+ offspring (early development – time w/ mom) • Learned behavior? Sponging Behavior in the Bottlenose Dolphin

  6. Learned behavior? • Difficulties in studying transmission of behavior • Approach  Dismiss alternative explanations • Eocological? • Spongers & nonspongers forage together • Genetic? • Evidence for genetic transimission (ncc) • If not  matrilineal social transmission likely Sponging Behavior in the Bottlenose Dolphin

  7. Random mating in Shark Bay • Coancestry coefficient of non-inbred individuals of same matriline approaches ZERO rapidly • If the haplotypes derived from ancient coancestry, relatedness of spongers should NOT be above average • If RECENT coancestry  HIGH relatedness • Genetically inherited? • OR • Culturally transmitted between relatives? Sponging Behavior in the Bottlenose Dolphin

  8. Behavioral Observations (1988-2002) • 9,029 boat surveys • 14,447 independent sightings • Identified spongers/non-spongers • Genetic Data from 185 dolphins • 13 adult spongers • Statistical Analyses • Dolphins from sponger area and close neighbors Materials & Methods

  9. Exclusion of genetic explanations? • Several possible modes of genetic inheritance • Tested against data on family level, pop. Level • Examine possibility of assortative (nonrandom) mating as explanation • If data does not support modes  • Cultural Transmission!?... Materials & Methods

  10. Haplotype: set of closely linked genetic markers present on one chromosome which tend to be inherited together, it is half the genotype. • Significant association between haplotype and sponging Results

  11. 8 different haplotypes in Shark Bay, 6 of which occur in the study area Results

  12. Significant non-random association between haplotype and sponging • Indicates sponging is mainly passed on within a single matriline Results

  13. 10 different modes of genetic inheritance Results

  14. 10 different modes of genetic inheritance Results

  15. Between 2001-2004 45 of the 65 adult males who overlapped with the sponging area consorted with 11 of the 12 female sponge carriers • At least 88.2% of offspring sired by non-sponge carrying males • No observed heterozygote deficit among all 13 spongers Results

  16. Discussion • Study qualifies as material culture in marine mammal species • Reasons: (1) not genetically passed (2) not assortative mating pass • Comes to the conclusion that it is culturally transmitted

  17. Not Genetic • Tool use is highly unlikely to be a direct behavior of a single locus of inheritance. • Not even multi loci inheritance. • Note: 10 different modes of genetic inheritance mentioned earlier (Table 3)

  18. Assortative Mating • Extremely unlikely! Why? • (1) Adult males almost never sponge • (2) Sponging females have been shown to conceive from nonsponging males • (3) Data show that almost all offspring of spongers are sired by nonsponging males • (4) They did not observe the predicted heterozygosity deficit in the sample(13). • *Note: small sample size of 13 is not statistically powerful but offers support against assortative mating.

  19. Why Cultural Transmission? • Bottlenose dolphins have shown to have high • cognitive skills • imitation skills • vocal learning. • Most importantly: Dolphins are highly capable of Social Learning in the wild and captivity • It is most likely a very new tool use behavior that is being passed down a matrilineal line.

  20. Strengths vs. Weaknesses • Strengths • High amount of observations over a long period of time • Clean genetic analysis • Good rejection of Assortative Mating Theory • A relatively new behavior that poses future research • Weaknesses - small concentrated sample - If it is culturally transmitted why do males rarely exhibit this behavior? - Possible combo of genes & culture

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