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No sex for Daphnia in the Italian Alps…

France Dufresne

1

, Adriana Bellati

2

, Rocco Tiberti

2,3

1Université du Québec à Rimouski, 300 allée des Ursulines G5L 3A1 Rimouski, Québec, Canada

2DSTA, Dipartimento di Scienze della Terra e dell’Ambiente, Università di Pavia, Via Ferrata 9 27100, Pavia, Italy

3Alpine Wildlife Research Centre, Parco Nazionale Gran Paradiso, Degioz 11, 11010 Valsavarenche, Aosta, Italy

Université du

Québec à Rimouski

Acknowledgments: This work was supported by funds from the Natural Sciences and Engineering Research Council of Canada (CRSNG),

le Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT) and le Centre d’Études Nordiques (CEN) and BIOAQUAE for sampling in the GPNP. We would thank Silvia Markova for European specimens. Logistic support was provided by the Gran Paradiso National Park within the framework of the LIFE+ project BIOAQUAE (Biodiversity Improvement of Aquatic Alpine Ecosystems, LIFE11BIOIT000020).

References: Beaton MJ, Hebert PDN. (1988) Geographical Parthenogenesis and Polyploidy in Daphnia pulex. Am. Nat. Vol. 132(6):

837-845; Bellati A, Tiberti R et al (2014) A dark shell hiding great variability: A molecular insight into the evolution and conservation of melanic Daphnia populations in the Alps. Zool J Linnean Soc. 171(4). Dufresne F, Hebert PDN. (1994) Hybridization and the origins of polyploidy.

Proc. Roy Soc. Ser. B. Vol. 258: 141-146; Dufresne F, Markova S, et al. Diversity in the Reproductive Modes of European Daphnia pulicaria

Deviates from the Geographical Parthenogenesis. PLOs One 6(5); Lynch M, Seyferth A et al. (2008) Localization of the Genetic Determinants of Meiosis Suppression in Daphnia pulex Genetics 180:317-327; Mergeay J, Aguilera X et al. (2008) The genetic legacy of polyploid Bolivian Daphnia: the tropical Andes as a source for the North and South American D. pulicaria complex. Molecular Ecology17:1789–1800.

Discussion

It is most likely that Daphnia inhabiting the four lakes in the Western Alps reproduce by obligate parthenogenesis as there is no clonal diversity and no males were observed in laboratory cultures.

Daphnia from GPNP had microsatellite genotypes that clustered in two different clades in the NJ tree. These results are congruent with a previous mtDNA study that showed that Daphnia from Lake Nivolet, Lake Trebecchi inferiore and Lake Trebecchi superiore belong to the boreal clade of European D. pulicaria whereas those from Lake Lillet were genetically distinct and belong to the alpine clade of European D. pulicaria.

The two clones were diploids as the other alpine clones of the High Tatra mountains.

How did transitions to obligate parthenogenesis occurred in these populations?

Preliminary results indicate that alleles that suppress meiosis in females but not in males as in North American Daphnia likely involved (as in Lynch et al. 2008).

Future studies using genomic tools will help to better assess genetic relationships among alpine and lowland populations of European D pulicaria. As well, gene expression studies comparing lowland and alpine populations are needed to decipher local adaptations to life in high altitude environments. Since impacts of human-related activities and climate changes on mountain species are known to be dramatic, we pose strong issues for the conservation of these extremely localized taxa.

Materials and methods

Introduction

Differential distribution of asexual species at high altitudes and latitudes has long been noted and coined geographical parthenogenesis. This pattern is thought to arise from the better colonization abilities of asexuals.

Daphnia appear to comply with this as subarctic and arctic species typically

reproduce by obligate parthenogenesis (Beaton & Hebert 1988, Dufresne & Hebert 1994). Some Daphnia populations from high altitudes are also known to reproduce asexually i.e. those in the Bolivian Andes (Mergeay et al. 2008) and also those in the High Tatra mountains (Dufresne et al. 2011). By contrast, although also inhabiting alpine environments, D. pulicaria from the Pyrenees reproduce primarily by cyclic parthenogenesis (Dufresne et al. 2011), suggesting complex glaciation history may play a role in transitions to asexuality.

This study aimed to determine the reproductive mode and clonal diversity patterns of Daphnia pulicaria from four lakes in the Italian Alps.

European D. pulicaria

ND5 tree of members of the Daphnia pulex complex

Lake Lillet

Haplotype network based on ND5 sequences (Bellati et al. 2014)

Lakes

Trebecchi and Nivolet

were sampled in Gran Paradiso, National Park (GPNP, Western Alps) including Lake Nivolet , Lake Trebecchi Inferiore, Lake Trebecchi Superiore, and Lake Lillet. The lakes are spatially very close to each other but belong to different river catchments: lake Lillet is situated in the Orco river basin, whereas the others three lakes are located within the Dora di Savarenche river catchment. 24 individuals per lake genotyped at six microsatellite loci (Dp183, Dp502, Dp512, Dp513, Dp514, Dp514alt). These genoypes were added to a previous set of genotypes from other alpine and lowland European sites (Dufresne et al. 2011). Alleles were transformed into a presence/absence matrix and Cavalli-Sforza chord distances were obtained and a neighbor-joining tree constructed using MEGA7.

Estat3 Rimova RimovB Rimov4 Petch2 Tchez6 Tchez10 Tchez7 Tchez8 Tchez9 Metis Lillet NTSMA NTSMB Litv4 Litv5 Nivolet Tresup Tresinf ZK21 ZK22 Slapy SpainPc Chme1 Czarnywh Czarny CHMELICE2 Bohda 0.05

Results

A single multilocus genotype among the 72 individuals

genotyped in Lakes Nivolet, Trebecchi Inferiore and

Trebecchi Superiore! Another multilocus genotype

among the 24 individuals from Lillet

From Lynch et al. 2008

Four alpine lakes were sampled in Gran Paradiso, National Park (GPNP, Western Alps) including Lake Nivolet, Lake Trebecchi Inferiore, Lake Trebecchi Superiore, and Lake Lillet. The lakes are spatially very close to each other but belong to different river catchments: lake Lillet is situated in the Orco river basin, whereas the others three lakes are located within the Dora di Savarenche river catchment. Four alpine lakes

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