Abstract
The association between the African ant plant, Vachellia drepanolobium, and the ants that inhabit it has provided insight into the boundaries between mutualism and parasitism, the response of symbioses to environmental perturbations, and the ecology of species coexistence. We use a landscape genomics approach at sites sampled throughout the range of this system in Kenya to investigate the demographics and genetic structure of the different partners in the association. We find that different species of ant associates of V. drepanolobium show striking differences in their spatial distribution throughout Kenya, and these differences are only partly correlated with abiotic factors. A comparison of the population structure of the host plant and its three obligately arboreal ant symbionts, Crematogaster mimosae, Crematogaster nigriceps, and Tetraponera penzigi, shows that the ants exhibit somewhat similar patterns of structure throughout each of their respective ranges, but that this does not correlate in any clear way with the respective genetic structure of the populations of their host plants. A lack of evidence for local coadaptation in this system suggests that all partners have evolved to cope with a wide variety of biotic and abiotic conditions.
Highlights
Few fields have benefited from the increasing ease of DNA sequencing as much as phylogeography, the study of the geographic distribution of genetic lineages (Beheregaray, 2008; Edwards et al, 2015)
We did not include a fourth ant associate, Crematogaster sjostedti, in our population genetic study because we found it on V. drepanolobium trees only in Laikipia, at two adjacent sites, Suyian Ranch and Mpala Research Centre
C. sjostedti was only found on V. drepanolobium trees in the northeastern sites of Suyian and Mpala
Summary
Few fields have benefited from the increasing ease of DNA sequencing as much as phylogeography, the study of the geographic distribution of genetic lineages (Beheregaray, 2008; Edwards et al, 2015). The population genetic dynamics of both partners in a symbiosis have been assessed in relatively few systems, primarily in macrobe-microbe interactions In such symbioses, a wide range of possible outcomes has been described: population structures may be broadly congruent, as in a fungus-beetle symbiosis (Roe et al, 2011) or certain kinds of lichen associations (Werth and Scheidegger, 2012; Widmer et al, 2012). A wide range of possible outcomes has been described: population structures may be broadly congruent, as in a fungus-beetle symbiosis (Roe et al, 2011) or certain kinds of lichen associations (Werth and Scheidegger, 2012; Widmer et al, 2012) Such congruence may signal specialized coevolution and reciprocal adaptation of populations of hosts and their respective symbionts, or may have other. In the ant-plant systems Leonardoxa africana (Léotard et al, 2009) or Barteria fistulosa (Blatrix et al, 2017), population genetic structure was largely congruent, while Yucca brevifolia showed more population divergence than its symbiont moths (Smith et al, 2011)
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