BIOL2609_L19_2007 - Molecular Ecology ECOL 2007 Lecture 19...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Molecular Ecology ECOL 2007 Lecture 19: Phylogeography: Gene flow among highly mobile populations Phylogeography of billfishes Billfish are successful predators in the epipelagic region Taxonomy of billfishes Family Istiophoridae Genus Makaira • M.nigricans (blue marlin) • M.indica (black marlin) Genus Istiophorus • I.platypterus (sailfish) Genus Tetrapturus • T.albidus (white marlin) • T.audax (striped marlin) • T.pfluegeri (longbill spearfish) • T.angusirostris (shortbill spearfish) • T.belone (Mediterranean spearfish) • T.georgei (roundscale spearfish) Family Xiphidae Genus Xiphias • X.gladius (swordfish) We will concentrate on the family Istiophoridae • Billfish are an important commercial and recreational fisheries resource – Catch of the genus Makaira alone was >40x103t in 1990 (FAO, UN) • They are fished commercially by long line, and are a considerable part of by-catch in tuna fishing operations • All billfish are categorized as: fully-exploited or over-exploited by ICCAT*, and so their continued fishing is not ecologically sound or sustainable – * = International Commission for the Conservation of Atlantic Tunas Non-molecular views on intraspecific population structure • Little was known of intraspecific population structure for any of the billfish • Assumed that due to mobility and continuous distribution – there would be little population subdivision between the oceans • Some tag-recapture data seemed to support this but based upon very few recoveries (0.5-2%) and unequal efforts in recovery at different locations • More recent molecular analysis has revealed considerable intraspecific genetic differentiation with location • Genetic variation vs location = phylogeography Striped marlin • Distribution: Pacific & Indian Ocean • Traditional studies (Squire & Suzuki 1990): single Pacific stock • However, RFLP analysis of mtDNA (Graves & McDowell 1994) suggests the existence of >1 Pacific population • ~40 fish per site • mtDNA haplotypes differed by 1-2 restriction site changes (nucleotide sequence divergence measured at 0.16-1.11%) • Phylogeographic analysis: genetic variability vs location • Revealed shallow structuring, consistent with evolutionarily recent restrictions to gene flow Striped marlin mtDNA haplotypes location Haplotype Mexico Ecuador Hawaii Australia A B C D E F G Unique Totals 12 6 8 0 0 0 6 4 36 20 6 9 2 1 1 0 1 40 14 7 4 10 2 0 0 6 43 12 3 1 8 7 11 0 5 47 Phylogeographic map of Pacific striped marlin Based upon 166 marlin samples, RFLP using 11 restriction endonucleases, circle size proportional to abundance of haplotype (smallest circle = 2 individuals) White marlin • Very similar to striped marlin • Atlantic distribution only • RFLP analysis of mtDNA from 3 sites (~15 fish per site) revealed no significant heterogeneity among white marlin (Graves & McDowell 1995) – unlike the striped marlin considered in the previous example • HOWEVER – white marlin territory overlaps with that of the striped marlin around South Africa – Two haplotypes are common to both species, acounting for 87% and 25% respectively – The other haplotypes were also similar, differing by only 1-2 restriction sites • This suggests that if striped and white marlin are valid species, then: they separated recently or, introgression has occurred since speciation Phylogeographic analysis of striped and white marlin Haplotypes included are 166 striped marlin & 52 white marlin, generated with 10 retsriction endonucleases Blue marlin The relationship of Atlantic and Indo-Pacific blue marlin has always been considered problematic • Single circum-tropical population Rivas 1975) • Atlantic & Indo-Pacific population (Nakamura 1985) – based on slight differences in lateral line morphology • Blue marlin exhibit considerable genetic variation (Graves & McDowell 1995) • RFLP analysis of mtDNA, using 11 restriction enzymes • Significant difference in haplotype distribution between Atlantic and Indo-Pacific • Also significant within-ocean population structure – E.g. one haplotype apparently confined to Atlantic fish was found in 11/74 Jamaican fish, but only 1/74 of nonJamaican Atlantic fish • This level of population structure is strange given the mobility of the fish – E.g. Tag/recapture suggests 10% W.Atlantic fish are recaptured in E.Atlantic • Why? – Spawning site fidelity? Phylogeographic analysis: • Reveals two groups of haplotypes that differ by several restriction site differences – Nucleotide divergence measured as 1.35% • One group of haplotypes was ubiquitous – Found in 55% Atlantic fish and all Indo-Pacific fish • Ten haplotypes were present in both Atlantic and Indo-Pacific fish • The remaining haplotypes (accounting for 45% of individuals caught) were found only in Atlantic fish • These two genetically divergent groups suggest historical isolation Phylogeographic analysis of Atlantic and Indo-Pacific blue marlin Included haplotypes from 138 Atlantic and 68 Pacific fish Sailfish As for blue marlin, the taxonomy of sailfish has been problematic: • Morrow & Harbo (1969) – single circumtropical species • Nakamura (1985) – two species based on morphology • RFLP of mtDNA from 56 Atlantic & 33 IndoPacific fish • Higher haplotype diversity in Atlantic fish • Accounted for by presence of two distinct groups of haplotypes, only one of which appeared in Indo-Pacific fish – These two groups were separated by 3 restriction site differences, and had nucleotide divergence of 0.65% • In contrast to blue marlin, the ubiquitous sailfish haplotypes were not found in high number among Atlantic fish • Only two haplotypes were shared between oceans, accounting for 76% of Indo-Pacific samples and 9% of Atlantic samples Phylogeographic analysis: • Similar pattern to blue marlin • Atlantic fish – two distinct haplotypes, only one of which is present in Indo-Pacific fish • How did this occur? – Extinction of intermediate haplotypes? - but unlikely to occur in both species – Long period of isolation between conspecific populations, coupled with recent unidirectional exchange? – possible as cool waters may have prevented inter-oceanic movement in the past Phylogeographic analysis of sailfish Haplotypes included are from 56 Atlantic and 33 Indo-Pacific fish ...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online