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Relatedness, body size and paternity in the alpine newt, Triturus alpestris

Trenton W. J. Garner and Benedikt R. Schmidt

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INTRODUCTION• Sexual-selection─Traditionallya. Females judge male quality via a trait or traits.(body size,

physical vigour and costly ornaments)b. A male that possesses the trait optimum represents the

best choice for every female.(Andersson 1994)

Q: Selection for a single optimum should rapidly exhaust any adaptive variation in a population?

Q: How adaptive genetic variation can be maintained in a population where strong sexual selection favours a certain phenotype?

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INTRODUCTION

• Sexual-selection─

Recentlya. Each individual female has her own ‘best’ mate.

b. The combination of male and female genotypes etermines the mate-choice optimum.

(Zeh 1996)

Adaptive genetic variation is maintained because each individual has its own best mate.

(Tregenza & Wedell 2000)

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INTRODUCTION• Males of the two newt species (Triturus vulgaris &T. crist

atus) develop large dorsal crests during the breeding season.

(Halliday 1977)

• Large-crested males are able to signal quality both through the height of the crest and the vigour of their courtship.

(Green 1991; Gabor & Halliday 1997)

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Triturus vulgaris male

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INTRODUCTION

Triturus alpestris─• Develop no or relatively small and invariant crests during

the breeding season. (Arntzen & Sparreboom 1989)

• Exhibit courtship behaviours that lack many of the strong vigour signals.

(Arntzen & Sparreboom 1989)

• Polyandry has been detected in this species.(Halliday 1998; Rafinski & Osikowski 2002)

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Triturus alpestris

Male

Female

8larva

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INTRODUCTION

Triturus alpestris─• The roles of phenotype and genotype in the mating sys

tem of T. alpestris?

(1) Does relatedness influence paternity?

(2) Does male body size influence paternity?

(3) Does female body size influence paternity?

(4) Does polyandry can influence offspring fitness?

fitness： fecundity and hatching success

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MATERIAL & METHODS

(a) Experimental protocol

Newts were collected after migrating to the pond verge but before entering the water.

↓

Measuremented their weight.

↓

Divided males into two groups. [large (L) and small (S)]

↓

Paired

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MATERIAL & METHODS

Pair patternMale(N=26)

Larger(L)( 1, 2, 3, 4,…13 )

Smaller(S)( 1, 2, 3, 4,…13 )

Female(N=13)

ML1 MS1 F??

Ramdam

+ +a trio

And so on (Total： 13 trios)

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MATERIAL & METHODS

↓

Trios were placed in plastic tubs filled to within several centimetres of the rim with aged water.

↓

After undisturbed for a 3 day, removed all males.

All males→cuted tail tip→frozan at -80℃

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MATERIAL & METHODS

↓

Trios were placed in plastic tubs filled to within several centimetres of the rim with aged water.

↓

After undisturbed for a 3 day, removed all males.

Placed anchored plastic strips into each tub(female will wrap their eggs in it). → Checked it every 1-3 days

At regular intervals, Added several Rana sp. larvae and zooplankton to each tub as food for females.

↓

↓

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MATERIAL & METHODS

↓

After 18 day,there were more than half of all female stopped depositing eggs.→Removed all females.

Eggs were kept indoors, in 0.5 l tubs containing aged tap water.

Larvae were sacrificed and stored individually at -80 °C for genetic analysis.

↓

↓

Recorded the total number of eggs and the total number of eggs hatching for each clutch.

↓

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MATERIAL & METHODS(b) Molecular analysis

DNA was extracted from tail tips and sacrificed larvae.

↓

PCR(Ta3Caga1 and Ta1Caga4.)

↓

Electrophoresed

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MATERIAL & METHODS(c) Data analysis

genetic similarity (r-values) between adults within trios.

Test the hypotheses that female mass, difference in mass among paired males and male relatedness to females affect the proportion of offspring sired.

↓using the program Kinship v. 1.3.1, with cross (1–13) as the group v

ariable and results displayed by group.

↓using a generalized linear model with binomial error.

Relatedness of males to females was entered into the model asa categorical variable (more versus less related)

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MATERIAL & METHODS(c) Data analysis

Tested whether multiply sired clutches are primarily fathered by a given relatedness category.

Tested for differences in fitness components between singly and multiply sired clutches.

↓Fisher’s exact test

↓Two-sample t-test.

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RESULTS

★★

1.The mean and variances of both fitness components did not differ significantly between multiply and singly sired

clutches.

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RESULTS

2. The relatedness of females to males had a statistically significant effect on the proportion of offspring sired. when it was entered as a continuous variable.

3. Female mass and difference in mass between the males did not significantly affect the proportion of offspring sired.

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DISCUSSION1. Paternity in the alpine newt is significantly influenced by parental genetic similarity butnot body size.

Female choice for inbreeding avoidance,and inbreeding avoidance has been implicated in a variety of mating systems.

Inbreeding negatively affects： reproductive output, survival, fitness….

Our study did not control for the number of permatophores transferred to the female. as was also the case with sand lizards (Olsson et al. 1996).

There is no sexual selection on male body size in these newts.

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DISCUSSIONLarger females did not exhibit more multiple paternity than smaller ones.

Female body size does not correlate significantly with the number of eggs deposited.so It is unlikely that increased male interest and affect paternity patterns.

Furthermore, pre-insemination, female preference for genetically dissimilar males.

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DISCUSSION2. Our comparison of multiply and singly sired clutches revealed no differences in fecundity or fertility.

Polyandry affords no fitness benefits to newts.

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DISCUSSIONIf less-related males are preferred, or, at least, more successful fathers, then why should females mate with more-related males?

Female multiple mating resulted in increased fecundity and fertility, and multiple mating is probably driven by fertility assurance.

(Osikowski &Rafinski 2001)

Benefits from multiple spermatophores may be detectable only over a longer mating and subsequent oviposition period than we provided.

Provides no evidence against the fertility-assurance hypothesis because of the experimental procedures.

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DISCUSSIONFemale mate choice in this species can be explained as a

form of pre-insemination mate choice for genetic compatibility:

(relies primarily on chemical communication and a female

preference for genetically dissimilar males.)

what is the phylogenetic distribution of female choice for genetic compatibility v.s. condition-dependent traits in the genus Triturus?

In future： 1. incorporating a phylogenetic approach focusing on the occurrence of female choice for genetic compatibility are required,

2. potentially confounding effects of fertility assurance need to be accounted for.

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Thanks for your attention