Population structure in the South American tern Sterna hirundinacea in the South Atlantic: two populations with distinct breeding phenologies

Abstract

The South American tern Sterna hirundinacea is a migratory species for which dispersal, site fidelity and migratory routes are largely unknown. Here, we used five microsatellite loci and 799 bp partial mitochondrial DNA sequences (Cytochrome b and ND2) to investigate the genetic structure of South American terns from the South Atlantic Ocean (Brazilian and Patagonian colonies). Brazilian and Patagonian colonies have two distinct breeding phenologies (austral winter and austral summer, respectively) and are under the influence of different oceanographic features (e.g. Brazil and Falklands/Malvinas ocean currents, respectively), that may promote genetic isolation between populations. Results show that the Atlantic populations are not completely panmictic, nevertheless, contrary to our expectations, low levels of genetic structure were detected between Brazilian and Patagonian colonies. Such low differentiation (despite temporal isolation of the colonies) could be explained by demographic history of these populations coupled with ongoing levels of gene flow. Interestingly, estimations of gene flow through Maximum likelihood and Bayesian approaches has indicated asymmetrical long term and contemporary gene flow from Brazilian to Patagonian colonies, approaching a source–sink metapopulation dynamic. Genetic analysis of other South American tern populations (especially those from the Pacific coast and Falklands–Malvinas Islands) and other seabird species showing similar geographical distribution (e.g. royal tern Thalasseus maximus), are fundamental in gaining a better understanding of the main processes involved in the diversification of seabirds in the southern hemisphere.

Speciation in seabirds: why are there so many species…and why aren’t there more?

“…Few other possible cases of population differentiation due to allochrony have been reported, and most populations that differ in breeding phenology also differ in other features such as ocean regime (e.g., South American Tern Sterna hirundinacea; Faria et al 2010). Furthermore, many colonies show strong breeding synchrony, and allochrony cannot occur in strongly seasonal ocean regimes.…”

The role of behavior in tern conservation

“…Dispersal results in gene flow between colonies and between geographic regions (Szczys et al, 2005;Draheim et al, 2010;Faria et al, 2010), and may also allow terns to respond quickly to changes in climate or other ecological factors (Møller et al, 2006). Lack of dispersal, on the other hand, contributes to genetic differentiation (Sruoga et al, 2006;Szczys et al, 2012;Boutilier et al, 2014) and can prevent recovery of genetic variation in small populations .…”

“…Because of the flight ability of terns, it is likely that any limits to immigration and emigration are behavioral rather than physical (Matthiopoulos et al, 2005;Faria et al, 2010). Behaviors that affect the frequency of movement among colony sites include site fidelity (philopatry), natal and breeding dispersal, and group adherence.…”

“…Although most research and management actions occur at breeding colonies, the largest current threat to many migratory tern populations may be mortality on the wintering grounds, rather than low productivity on the breeding grounds (Nisbet and Spendelow, 1999;Wendeln and Becker, 1999c;Shealer et al, 2005;Cabot and Nisbet, 2013). Conditions at the wintering grounds, such as food availability, may also have effects that carry-over to the breeding season (Møller et al, 2006), and shared wintering areas can provide opportunities for pairing among conspecifics from geographically isolated breeding areas (Faria et al, 2010). Discrete staging areas where entire regional populations may gather after breeding and before migration have been discovered: roseate terns of the northeastern United States and Canada at and near Cape Cod, USA (Trull et al, 1999;Jedrey et al, 2010) and black terns of Europe and western Asia in and around IJsselmeer, the Netherlands and Sivash, Ukraine (Van der Winden, 2003).…”

Use of molecular genetics for understanding seabird evolution, ecology and conservation

“…For example, Boessenkool et al (2009) used multilocus assignments in their study of yelloweyed penguins Megadyptes antipodes and found evidence of rare migration events that would not likely have been detected otherwise. Similarly, Hall et al (2009) used molecular assignments to characterize dispersal patterns in marbled murrelets Brachyramphus marmoratus in central California, and Faria et al (2010) used both molecular assignments and methods based on coalescent theory to infer source− sink dynamics in South American terns Sterna hirundinacea. In an innovative modification of molecular assignments known as parent-offspring dyad analysis, Peery et al (2008) determined that the central California population of marbled murrelets is a demographic sink.…”