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Genetic variation and local adaptation in peripheral populations of toads
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för ekologi och evolution, Populationsbiologi och naturvårdsbiologi.ORCID-id: 0000-0002-5553-2691
2009 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Northern fringe populations generally have low amounts of genetic variation and inhabit habitats where specific adaptations are needed. On the Swedish west coast, the natterjack toad (Bufo calamita) inhabits skerry islands. I have examined: I) adaptation to two environmental stressors in this habitat; II) the genetic population structure within the skerry habitat; III) the effects of neutral genetic variation, selection and genetic drift on trait divergence within the skerry habitat; and IV) the effects of genetic variation on fitness under three thermal conditions of varying stressfulness. V) I have also studied the impact of putative local adaptations on the Scandinavian green toad (Bufo viridis) conservation programme. The results suggest that the skerry natterjack toads are locally adapted to the desiccation risk in their habitat. However, despite inhabiting a more saline habitat, they had a lower salinity tolerance when compared to their conspecifics in the more general habitat. The lowered salinity tolerance is most likely explained by the presence of negative genetic correlations between salinity tolerance and desiccation avoidance and suggests that the occurrence of multiple environmental stressors may constrain adaptation. Within the skerry habitat, the toads exhibited a strong population structure with populations differing in their levels of genetic variation. Moreover, within the skerry habitat, the results suggest uniform selection pressures. However, correlations between trait values and neutral genetic variation suggest that inbreeding depression may affect trait values and thus potentially constrain adaptation. In the natterjack toad, fitness costs associated with lack of genetic variation were only present under benign conditions and not under more natural conditions. This suggests that environmental stress masks inbreeding depression in these traits under natural conditions. In the study regarding the Scandinavian green toads, I found that one population inhabiting a saline habitat had a higher salinity tolerance than other populations in less saline habitats. This suggests the presence of local adaptation, which should be acknowledged in the green toad conservation programme. Several of the northern fringe populations of toads fulfill the criteria of being Evolutionary Significant Units and their conservation thus should be prioritized.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis , 2009. , s. 65
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 662
Nationell ämneskategori
Ekologi
Forskningsämne
Populationsbiologi
Identifikatorer
URN: urn:nbn:se:uu:diva-107395ISBN: 978-91-554-7580-2 (tryckt)OAI: oai:DiVA.org:uu-107395DiVA, id: diva2:229129
Disputation
2009-09-25, Friessalen, Norbyvägen 18A, Uppsala, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2009-09-04 Skapad: 2009-08-10 Senast uppdaterad: 2015-04-29Bibliografiskt granskad
Delarbeten
1. The interaction of multiple environmental stressors affects adaptation to a novel habitat in the natterjack toad Bufo calamita
Öppna denna publikation i ny flik eller fönster >>The interaction of multiple environmental stressors affects adaptation to a novel habitat in the natterjack toad Bufo calamita
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2009 (Engelska)Ingår i: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 22, nr 11, s. 2267-2277Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The potential to adapt to novel environmental conditions is a key area of interest for evolutionary biology. However, the role of multiple selection pressures on adaptive responses has rarely been investigated in natural populations. In Sweden, the natterjack toad Bufo calamita inhabits two separate distribution areas, one in southernmost Sweden and one on the west coast. We characterized the larval habitat in terms of pond size and salinity in the two areas, and found that the breeding ponds of the western populations run higher desiccation risk and had higher salinity than the ponds used by the southern populations. In a common garden experiment manipulating salinity and temperature, we found that toads from the west coast populations were locally adapted to shorter pond duration as indicated by their higher development and growth rates. However, despite being subjected to higher salinity stress in nature, west coast toads had a poorer performance in saline treatments. We found that survival in the saline treatments in the west coast populations was positively affected by larger body mass and longer larval period. Furthermore, we found negative genetic correlations between body mass and growth rate and their non-adaptive plastic responses to salinity. These results implicate that the occurrence of multiple environmental stressors needs to be accounted for when assessing the adaptive potential of organisms and suggest that genetic correlations may play a role in constraining adaptation of natural populations.

Nyckelord
Trade-offs, genetic correlations, evolutionary change, natural selection, life-history traits
Nationell ämneskategori
Biologiska vetenskaper
Forskningsämne
Populationsbiologi
Identifikatorer
urn:nbn:se:uu:diva-107340 (URN)10.1111/j.1420-9101.2009.01842.x (DOI)000271049500013 ()
Tillgänglig från: 2009-08-06 Skapad: 2009-08-06 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
2. Genetic structure in peripheral populations of the natterjack toad, Bufo calamita, as revealed by AFLP
Öppna denna publikation i ny flik eller fönster >>Genetic structure in peripheral populations of the natterjack toad, Bufo calamita, as revealed by AFLP
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2010 (Engelska)Ingår i: Conservation Genetics, ISSN 1566-0621, E-ISSN 1572-9737, Vol. 11, nr 1, s. 173-181Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Decreased fitness due to loss of genetic variation is a well recognised issue in conservation biology. Along the Swedish west coast, the endangered natterjack toad (Bufo calamita) occurs on, for the species, highly unusual habitat of rocky islands. Although the toads inhabit a restricted geographical area (maximum distance between the populations is 71 km), the fragmented nature of the landscape makes the genetic properties of the populations of conservation interest. However, lack of genetic variation found using conventional methods (microsatellites) has impeded genetic studies within these peripheral populations so far. In this study we assess population structure and genetic variation among seven of these fringe populations using 105 polymorphic Amplified Fragment Length Polymorphism (AFLP) loci. We found a well-defined population structure without evidence for isolation by distance, implying restricted gene flow between populations. Additionally, the populations differed in their amount of genetic variation, emphasizing the need to monitor genetically impoverished populations for possible declines mediated by inbreeding depression and reduced adaptive potential. Conservation implications for these unique populations are discussed in the light of our results.

Nyckelord
AFLP, genetic structure, peripheral populations, genetic diversity, amphibians
Nationell ämneskategori
Ekologi
Forskningsämne
Populationsbiologi
Identifikatorer
urn:nbn:se:uu:diva-107341 (URN)10.1007/s10592-009-0021-z (DOI)000273744300015 ()
Tillgänglig från: 2009-08-06 Skapad: 2009-08-06 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
3. The effects of selection, drift and genetic variation on life-history trait divergence among insular populations of natterjack toad, Bufo calamita
Öppna denna publikation i ny flik eller fönster >>The effects of selection, drift and genetic variation on life-history trait divergence among insular populations of natterjack toad, Bufo calamita
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2010 (Engelska)Ingår i: Molecular Ecology, ISSN 0962-1083, E-ISSN 1365-294X, Vol. 19, nr 11, s. 2229-2240Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Although loss of genetic variation is frequently assumed to be associated with loss of adaptive potential, only few studies have examined adaptation in populations with little genetic variation. On the Swedish west coast, the northern fringe populations of the natterjack toad Bufo calamita inhabit an atypical habitat consisting of offshore rock islands. There are strong among-population differences in the amount of neutral genetic variation, making this system suitable for studies on mechanisms of trait divergence along a gradient of within-population genetic variation. In this study, we examined the mechanisms of population divergence using Q(ST)-F-ST comparisons and correlations between quantitative and neutral genetic variation. Our results suggest drift or weak stabilizing selection across the six populations included in this study, as indicated by low Q(ST)-F-ST values, lack of significant population x temperature interactions and lack of significant differences among the islands in breeding pond size. The six populations included in this study differed in both neutral and quantitative genetic variation. Also, the correlations between neutral and quantitative genetic variation tended to be positive, however, the relatively small number of populations prevents any strong conclusions based on these correlations. Contrary to the majority of Q(ST)-F-ST comparisons, our results suggest drift or weak stabilizing selection across the examined populations. Furthermore, the low heritability of fitness-related traits may limit evolutionary responses in some of the populations.

Nyckelord
conservation biology, environmental stress, evolutionary change, genetic drift, life-history traits, natural selection
Nationell ämneskategori
Ekologi
Forskningsämne
Populationsbiologi
Identifikatorer
urn:nbn:se:uu:diva-107343 (URN)10.1111/j.1365-294X.2010.04642.x (DOI)000277975300005 ()20465584 (PubMedID)
Tillgänglig från: 2009-08-06 Skapad: 2009-08-06 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
4. Fitness costs associated with low genetic variation are reduced in a harsher environment in amphibian island populations
Öppna denna publikation i ny flik eller fönster >>Fitness costs associated with low genetic variation are reduced in a harsher environment in amphibian island populations
2010 (Engelska)Ingår i: Conservation Genetics, ISSN 1566-0621, E-ISSN 1572-9737, Vol. 11, nr 2, s. 489-496Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm)) Published
Abstract [en]

A basic premise of conservation geneticists is that low levels of genetic variation are associated with fitness costs in terms of reduced survival and fecundity. These fitness costs may frequently vary with environmental factors and should increase under more stressful conditions. However, there is no consensus on how fitness costs associated with low genetic variation change under natural conditions in relation to the stressfulness of the environment. On the Swedish west coast, natterjack toad Bufo calamita populations show a strong population genetic structure and large variation in the amount of within-population genetic variation. We experimentally examined the survival of natterjack larvae from six populations with different genetic variation in three thermal environments corresponding to (a) the mean temperature of natural ponds (stable, laboratory), (b) a high temperature environment occurring in desiccating ponds (stable, laboratory) and (c) an outdoor treatment mimicking the natural, variable thermal conditions (fluctuating, semi-natural). We found that larvae in the outdoor treatment had poorer survival than larvae in the stable environments suggesting that the outdoor treatment was more stressful. Overall, populations with higher genetic variation had higher larval survival. However, a significant interaction between treatments and genetic variation indicated that fitness costs associated with low genetic variation were less severe in the outdoor treatment. Thus, we found no support for the hypothesis that fitness costs associated with low genetic variation increase under more stressful conditions. Our results suggest that natural thermal stress may mask fitness losses associated with low genetic variation in these populations.

Nyckelord
Conservation genetics, genetic structure, peripheral populations, genetic diversity, amphibians, environmental stress
Nationell ämneskategori
Ekologi
Forskningsämne
Populationsbiologi
Identifikatorer
urn:nbn:se:uu:diva-107342 (URN)10.1007/s10592-009-0039-2 (DOI)000275455700013 ()
Tillgänglig från: 2009-08-06 Skapad: 2009-08-06 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
5. Population divergence of life history traits in the endangered green toad: implications for a support release programme
Öppna denna publikation i ny flik eller fönster >>Population divergence of life history traits in the endangered green toad: implications for a support release programme
2011 (Engelska)Ingår i: Journal of Zoology, ISSN 0952-8369, E-ISSN 1469-7998, Vol. 285, nr 1, s. 46-55Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

There is an increasing awareness that adaptive differences among local populations may affect the success of translocation programmes. A mismatch in habitat quality of the target localities and in the local adaptations of the translocated individuals may reduce the success rate of the translocation programme. The green toad Bufo viridis is the most threatened amphibian in Sweden and has been the focus of an extensive translocation programme of eggs, tadpoles and juvenile toads to several localities with apparently favourable conditions for green toads. However, the success of these measures has been poor. In this study, we investigated the extent of local adaptation in the green toad by examining population divergence and the effect of thermal and saline conditions on larval performance in four Scandinavian populations. In a common garden experiment, we measured larval survival and development as well as the occurrence of spinal deformations. In addition, we quantified pond temperature and water salinity, two important environmental variables for larval performance in anurans in the breeding ponds as well as in seven additional localities included in the conservation programme. We found significant variation among the localities in water temperature and salinity, and significant among-population divergence in larval life history traits and spinal deformations, including both trait means and plastic responses to salinity and temperature. The available evidence suggests that at least part of this divergence is adaptive. We did not find direct support for local adaptation affecting the success of the translocations, however, we argue that the population origin and the impact of rearing conditions on the fitness-related larval traits should be taken into account in the introduction measures of the Swedish green toad conservation programme as well as in translocation programmes in general.

Nyckelord
Local adaptation, conservation, peripheral populations, genetic diversity, amphibians
Nationell ämneskategori
Ekologi
Forskningsämne
Populationsbiologi
Identifikatorer
urn:nbn:se:uu:diva-107394 (URN)10.1111/j.1469-7998.2011.00843.x (DOI)000294170500006 ()
Tillgänglig från: 2009-08-10 Skapad: 2009-08-10 Senast uppdaterad: 2017-12-13Bibliografiskt granskad

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