Gene flow and genetic structure of Bactrocera carambolae (Diptera, Tephritidae) among geographical differences and sister species, B. dorsalis, inferred from microsatellite DNA data

Abstract

The Carambola fruit fly, Bactrocera carambolae, is an invasive pest in Southeast Asia. It has been introduced into areas in South America such as Suriname and Brazil. Bactrocera carambolae belongs to the Bactrocera dorsalis species complex, and seems to be separated from Bactrocera dorsalis based on morphological and multilocus phylogenetic studies. Even though the Carambola fruit fly is an important quarantine species and has an impact on international trade, knowledge of the molecular ecology of Bactrocera carambolae, concerning species status and pest management aspects, is lacking. Seven populations sampled from the known geographical areas of Bactrocera carambolae including Southeast Asia (i.e., Indonesia, Malaysia, Thailand) and South America (i.e., Suriname), were genotyped using eight microsatellite DNA markers. Genetic variation, genetic structure, and genetic network among populations illustrated that the Suriname samples were genetically differentiated from Southeast Asian populations. The genetic network revealed that samples from West Sumatra (Pekanbaru, PK) and Java (Jakarta, JK) were presumably the source populations of Bactrocera carambolae in Suriname, which was congruent with human migration records between the two continents. Additionally, three populations of Bactrocera dorsalis were included to better understand the species boundary. The genetic structure between the two species was significantly separated and approximately 11% of total individuals were detected as admixed (0.100 ≤ Q ≤ 0.900). The genetic network showed connections between Bactrocera carambolae and Bactrocera dorsalis groups throughout Depok (DP), JK, and Nakhon Sri Thammarat (NT) populations. These data supported the hypothesis that the reproductive isolation between the two species may be leaky. Although the morphology and monophyly of nuclear and mitochondrial DNA sequences in previous studies showed discrete entities, the hypothesis of semipermeable boundaries may not be rejected. Alleles at microsatellite loci could be introgressed rather than other nuclear and mitochondrial DNA. Bactrocera carambolae may be an incipient rather than a distinct species of Bactrocera dorsalis. Regarding the pest management aspect, the genetic sexing Salaya5 strain (SY5) was included for comparison with wild populations. The SY5 strain was genetically assigned to the Bactrocera carambolae cluster. Likewise, the genetic network showed that the strain shared greatest genetic similarity to JK, suggesting that SY5 did not divert away from its original genetic makeup. Under laboratory conditions, at least 12 generations apart, selection did not strongly affect genetic compatibility between the strain and wild populations. This knowledge further confirms the potential utilization of the Salaya5 strain in regional programs of area-wide integrated pest management using SIT.

Resolving cryptic species complexes of major tephritid pests

“…Admixture is evidence that some gene flow (i.e. hybridisation) may occur in the field between these species (Aketarawong et al 2015). …”

“…Molecular protocols using neutral genetic markers to distinguish the two species from each other, and from other closely related taxa, are provided in Boykin et al (2014). Microsatellite markers which amplify for both species and which are used in population genetic studies, are provided in Aketarawong et al (2015). The Y-specific marker will also separate the two species.…”

In the footsteps of Wallace: population structure in the breadfruit fruit fly, Bactrocera umbrosa (F.) (Diptera: Tephritidae), suggests disjunction across the Indo‐Australian Archipelago

“…Asia; Hu et al 2008;Aketarawong et al 2015) or across regions where the insect is native to one region and invasive in the second (e.g. Asia; Hu et al 2008;Aketarawong et al 2015) or across regions where the insect is native to one region and invasive in the second (e.g.…”

“…As part of ongoing research to understand the diversification of Bactrocera, a super-diverse genus of 461 species (Doorenweerd et al 2018), we investigated the population structuring of B. umbrosa as a representative of the small handful of Bactrocera species which cross the Asia-Pacific divide. Nearly all previous studies on intra-specific population structuring in Bactrocera and related fruit flies have found little or no evidence for historical biogeographic barriers playing a role in current population structuring, rather structuring is instead characterised by isolation-by-distance, geographical clines and/or disjunctions caused by modern invasion events (Virgilio et al 2010a;Aketarawong et al 2015;Boontop et al 2017). Studies on B. dorsalis (Hendel) (Krosch et al 2013) and Zeugodacus cucurbitae (Coquillet) (Boontop et al 2017), investigating the potential impact of the Isthmus of Kra seawaya major biogeographic barrier associated with the separation of the Oriental and Sunda biotas (Woodruff 2010)failed to detect any population structuring associated with the barrier.…”

“…All previous studies on population structuring in Dacini fruit flies across major biogeographic regions have focused within a region (e.g. Asia; Hu et al 2008;Aketarawong et al 2015) or across regions where the insect is native to one region and invasive in the second (e.g. Asia/Africa (Khamis et al 2009;Virgilio et al 2010a), Asia/Pacific (Boontop et al 2017a;Dupuis et al 2018)).…”