Genetic diversity and differentiation among insular honey bee populations in the southwest Indian Ocean likely reflect old geographical isolation and modern introductions

Abstract

With globalization the Western honey bee has become a nearly cosmopolitan species, but it was originally restricted to the Old World. This renowned model of biodiversity has diverged into five evolutionary lineages and several geographic “subspecies.” If Apis mellifera unicolor is indubitably an African subspecies endemic to Madagascar, its relationship with honey bees from three archipelagos in the southwest Indian Ocean (SWIO) hotspot of biodiversity is misunderstood. We compared recent mtDNA diversity data to an original characterization of the nuclear diversity from honey bees in the Mascarenes and Comoros archipelagos, using 14 microsatellites, but also additional mtDNA tRNALeu-cox2 analysis. Our sampling offers the most comprehensive dataset for the SWIO populations with a total of 3,270 colonies from 10 islands compared with 855 samples from Madagascar, 113 from Africa, and 138 from Europe. Comprehensive mitochondrial screening confirmed that honey bees from La Réunion, Mauritius, and Comoros archipelagos are mainly of African origin (88.1% out of 2,746 colonies) and that coexistence with European lineages occurs only in the Mascarenes. PCA, Bayesian, and genetic differentiation analysis showed that African colonies are not significantly distinct on each island, but have diversified among islands and archipelagos. FST levels progressively decreased in significance from European and African continental populations, to SWIO insular and continental populations, and finally among islands from the same archipelago. Among African populations, Madagascar shared a nuclear background with and was most closely related to SWIO island populations (except Rodrigues). Only Mauritius Island presented clear cytoplasmic disequilibrium and genetic structure characteristic of an admixed population undergoing hybridization, in this case, between A. m. unicolor and A. m. ligustica, A. m. carnica and A. m. mellifera-like individuals. Finally, global genetic clustering analysis helped to better depict the colonization and introduction pattern of honey bee populations in these archipelagos.

When European meets African honeybees (Apis mellifera L.) in the tropics: Morphological changes related to genetics in Mauritius Island (South-West Indian Ocean)

“…In the shorter term, increased genetic and phenotypic variances could have improved its ability to cope with growing anthropogenic threats, as illustrated by the recent and accidental introduction of Varroa destructor in Mauritius [94], a mite implicated in elevated colony mortality rates worldwide as a virus vector [95,96]. Thus, results presented by Techer et al [39,40] and here can beneficiate, as a reference point before V. destructor arrival, to the management of the honeybee in Mauritius in order to preserve its ecosystem and economic roles. More widely, it could provide better understanding on the impact of intraspecific hybridization and contact with new parasites on evolutionary trajectories of populations.…”

“…Recent genetic work by Técher et al [39,40] has shown that the population of Mauritius consists of two hybridizing genetic clusters: one African related to A. m. unicolor, whose origin (natural or anthropogenic) is not fully elucidated, and another European from successive imports. In order to better depict the honeybee population of Mauritius, the same bees were used for this study.…”

“…It offers the opportunity to study the effects of relatively recent hybridization on traits variability in tropical and insular environmental conditions. Latest genetic studies confirmed that the initial honeybee population of Mauritius belongs to the African lineage, closely related to A. m. unicolor [37] subspecies, endemic of Madagascar and established in surrounding archipelagos [38][39][40]. Mitochondrial signatures of repeated importations of European continental subspecies in the current population have been detected, and the analyses of genetic diversity revealed the occurrence of two hybridizing gene pools, with European and African ancestries sampled in near-balanced proportions (about 55% of A lineage, 44% of European C lineage, 1% of European M lineage) [39].…”

Shiga‐toxigenic Escherichia coli of cattle origin represents a surveillance priority and an important human health threat to public and travelers of the Indian Ocean islands

“…However, the lack of denominator (STEC infections) does not permit calculation of prevalence and incidence of STEC‐related cases in the Indian Ocean region. In the South‐West of the Indian Ocean region exists three archipelagos that lies near Madagascar: Comoros, Seychelles, and the Mascarene (Mauritius, Réunion, and Rodrigues) (Techer et al, ). Oceanic islands attract more and more tourists for their beautiful beaches, cultures, stunning landscapes, and unusual biodiversity (Messerli et al, ).…”

Autosomal and Mitochondrial Adaptation Following Admixture: A Case Study on the Honeybees of Reunion Island

“…A study of the genetic structure of the Reunion honeybee population, sampling >2,000 honeybees throughout the island and following standard methods ( Evans et al 2013 ) employing microsatellite markers and sequences of the tRNAleu-cox2 hyper-variable region, revealed an absence of population structure, despite the island’s various climate zones ( Techer MA, in press ). This contrasts for instance with the east–west distribution of genetic clusters of the melon fly Bactrocera cucurbitae ( Jacquard et al 2013 ).…”