Genetically distinct coelacanth population off the northern Tanzanian coast

Abstract

Since the sensational discovery of a living coelacanth off the east coast of South Africa, the geographic distribution of viable coelacanth populations has been a subject of debate. In the past, the coelacanths off the African mainland were thought to be strays from the Comoros because most coelacanths captured were caught in the waters surrounding the Comoros archipelagos. However, in recent years, a large number of coelacanths were captured off the coast of Tanzania, including nine living specimens observed in a remotely operated vehicles survey. Thus, it is possible that there is a reproducing population inhabiting waters off the Tanzania coast. We have sequenced the complete mitochondrial genomes of 21 Tanzanian and 2 Comoran coelacanths and analyzed these sequences together with two additional full mitochondrial genomes and 47 d-loop sequences from the literature. We found that the coelacanth population off the northern Tanzanian coast is genetically differentiated from those of the southern Tanzania coast and the Comoros, whereas no significant genetic differentiation occurs between the latter two localities. The differentiation between the northern and southern Tanzanian coast populations is consistent with the hypothesis that the existence of northward-flowing ocean current along the Tanzanian coast may reduce or prevent gene flow from the northern to the southern population. Finally, we estimated that the population localized to the southern Tanzanian coast and the Comoros diverged from other coelacanths at least 200,000 y ago. These results indicate that the coelacanths off the northern Tanzania coast are not strays but a genetically distinct group. Our study provides important information for the conservation of this threatened “living fossil.”

Coelacanth genomes reveal signatures for evolutionary transition from water to land

“…First, we constructed the reference coelacanth draft genome from one of the Tanzanian specimens (TCC041-004, gender unknown) (Nikaido et al 2011), which was recovered from the body cavity of its mother (coelacanths give birth to fully formed offspring) (Fig. 2).…”

“…In addition to the Comoros archipelagos, several coelacanths have been captured off the coasts of Mozambique (Schliewen et al 1993), Madagascar (Heemstra et al 1996), Kenya (De Vos and Oyugi 2002), and Tanzania (Sasaki et al 2007). Nikaido et al (2011) recently demonstrated that a coelacanth population off the northern coastal region of Tanzania is genetically distinct from that of Comoros, indicating that the northern coastal region of Tanzania is the second habitat of coelacanths in the western Indian Ocean. Furthermore, two coelacanth individuals (L. menadoensis) were also captured off the coast of Manado, Sulawesi, Indonesia (Erdmann et al 1998), on the opposite side of the Indian Ocean (the locations of the captured and observed coelacanths are summarized in Fig.…”

Why coelacanths are not ‘living fossils’

“…The first study [11] concluded that the low allelic diversity is the result of a small population size and the absence of strong geographic isolation, as has been concluded for similar findings in other species [14]. In contrast, the more recent study, Lampert et al [7], rejected these straightforward hypotheses.…”

“…Two population genetics studies in Latimeria chalumnae are available and both show low allelic diversity and low levels of geographic differentiation [7,11]. For neutral alleles, diversity depends on two opposite forces, the rate of mutation that is the source of new alleles and the genetic drift that eliminates alleles.…”

Single-male paternity in coelacanths

“…However, recent population genetic studies revealed genetic divergence between individuals among and within the field sites and thus a potential for adaptation in L. chalumnae 18,19 . Still they present an opportunity to get fascinating insights into the ecology and behaviour of a very old animal group.…”