RAD genetic mapping of reproductive mode in tadpole shrimps
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T. Mathers, R. Hammond, R. Jenner, A. Gómez
The Notostraca (Tadpole shrimps)
•An ancient order containing two genera: Triops and
Lepidurus.
•Around 15 described species. Species and genus diversity of Anostraca (An), Notostraca (Not), Spinicaudata (Spin) and Laevicaudata (Laev) in each of the seven zoogeographical regions. PA, Palaearctic; NA, Nearctic; NT, Neotropical; AT, Afrotropical; OL, Oriental; AU, Australasian; PAC, Pacific Oceanic Islands; ANT, Antarctic (Adapted from Brendonck et al Hydrobiologia 595 (2008)).
•They live in ephemeral pools and survive periods of drought through highly resistant cysts that can lay dormant for many years.
•This also makes them ideal for...
Grow your own living fossil
The reproductive modes of the Notostraca
Androdioecy is rare in animals
• Only a handful of animals share this rare breeding system:
(a) some barnacles
(b) Caenorhabditis elegans
(c) Kryptolebias (=Rivulus) marmoratus
(d) Eulimnadia (clam shrimps)
(e) Notostraca
• Potentially a transitional state between dioecy and hermaphroditism.
a
a
b
c
c
d
e
Barnacles
Androdioecy
Clam shrimps
Tadpole shrimps
JC Regier et al. Nature 000, 1‐5 (2010) doi:10.1038/nature08742
Phylogenetic relationships of 75 arthropod and five outgroup species
Androdioecy has evolved only once in Eulimnadia
28S tree derived from Bayesian analysis showing ancient origin of AD in Eulimnadia (Weeks et al Proc. R. Soc. B. 273 (2006)).
Between species variation in reproductive mode within the Notostraca and the evolution of androdioecy Triops
Lepidurus
Maximum likelihood tree, created in PhyML, based on a supermatrix of COI, 12S, 16S and elongation factor 1 alpha sequence data with reproductive mode mapped on using Mesquite. Inferred ancestral states are based on parsimony.
Modified from: Zierold et al. BMC Evolutionary Biology
2007 7:161 doi:10.1186/1471‐2148‐7‐161
Within species variation in reproductive mode of the European tadpole shrimp, Triops cancriformis
• Reproductive mode varies between populations of Triops cancriformis.
• Dioecious, hermaphroditic and androdioecious populations are all found.
What is the genetic basis for variation in reproductive mode?
• No obvious sex chromosomes have been described in the Notostraca.
• In Triops cancriformis 2n = 12
a = female b = male. Adapted from Ombretta et al. Caryologia 2005 58: 164 – 170.
However...
Weeks & Zucker (1999) Can. J. Zool. 77: 1402–1408
• In androdioecious Eulimnadia and Triops sex has been shown to be determined by a recessive male allele / linkage group / chromosome with two types of hermaphrodites ‐ monogenics and amphigenics. Nothing else is known about the genetics of sex determination or
reproductive mode.
Genetic mapping of reproductive mode
• We therefore intend to use RAD sequencing to create a linkage map of reproductive mode for Triops cancriformis.
• This will be achieved by obtaining an F2 generation from self fertilised F1 individuals that are the result of interpopulation crosses.
• Although inbred lines are not available T. cancriformis populations are highly differentiated and highly homozygous. Experimental design – mapping crosses
Hermaphrodite
Monogenic
(Austria ‐ hermaphroditic)
SS
Male
(Königswartha ‐ androdioecious)
ss
X
Out crossing
Hermaphrodite
Amphigenic
Ss
F1
I.D. of out crossed F1 progeny using available microsatellite markers
Self fertilisation in isolation
F2
Expected proportion of offspring
Hermaphrodite
Monogenic
SS
25%
Hermaphrodite
Amphigenic
Ss
Male
50%
25%
ss
Rearing and sexing of F2
RAD sequencing of parents and offspring
• We aim to sequence 2 parentals and 96 offspring using 6 lanes of Illumina sequencing.
• Parentals will be sequenced separately to estimate and characterise the number of segregating, polymorphic markers (SNPs and restriction site polymorphisms).
• F2 offspring will be barcoded and multiplexed (24 per lane).
Outcomes...
• These data will be used to create a genetic linkage map for Triops cancriformis that will be used to infer the genetic basis of reproductive mode variation. • The project will provide a genomic basis for future work investigating the evolution of reproductive modality across the whole group.
Acknowledgments
• Thanks to:
– My supervisors: Africa Gomez, Rob Hammond and Ronald Jenner
– Hull evolution group
– Thorid Zierold
– NERC
– NHM
– People who have sent samples
Towards a resolved Notostracan phylogeny
Triops
Lepidurus
Maximum likelihood Notostracan phylogeny based on a supermatrix alignment of COI, 12S, 16S and elongation factor 1 alpha incorporating GenBank data. Created using PhyML. Numbers in red show likelihood support values for branches.
Androdioecy in the Branchiopoda
Bisexual,
Bisexual
(androdioecious,
(parthenogenesis)
hermaphroditic)
ZZ, ZW
ZZ,ZW?
Anostraca
Notostraca
Bisexual
?
Laevicaudata
Multiple times
Bisexual,
(androdioecious,
hermaphroditic)
ZZ, ZW
ss, Ss, SS
Spinicaudata
Once
Cyclical parthenogenesis
(environmental)
Cladoceromorpha