presentacion Antonio (lluis) (versione definitiva) pdf

Testing trophic niche partitioning in sibling species: A stable isotope study of Dysdera spiders in the

Eastern Canary islands

Departamento de Biologia animal

Estudiante: Antonio Sanna

Directores: Carolina Sanpera Trigueros Miquel Arnedo Lombarte

Màster de Biodiversitat 2014 / 2015

• Dysdera : >250 species Circum-Mediterranean distribution (Central Asia – Macaronesian Islands)

• ground-dwelling ,nocturnal wandering, hunter spiders (isopodos)

• Important diversification in the Canary Islands (>50 endemics)

The spider genus Dysdera in the Eastern Canary Islands

Some in sympatry

The studied species

D.alegranzaensis

D.nesiotes

D.mahan

No morphological differences , except for genitalia

Objective of the study

• Testing resource partitioning in similar sympatric species: D.alegranzaensis and D.nesiotes

• Testing the use of resources from marine origin in the species with coastal habitat D.mahan

The stable isotope analysis

The stable isotopes used :

• The δ15N ( 15N/14N): (3-4 ‰) trophic level shift

It depends on the base of food wed (isotopic baseline)

• The δ 13C (13C/12C): (0.5 ‰) lower change with trophic level

Major changes related to carbon source:

terrestrial < marine environment

C3 plants (-27 ‰) < C4 plants (-12‰)

Use of δ15N and δ 13C as biomarkers of ecological dimensions

HYPOTHESIS

Hypothesis 1: DA and DN should have different isotopic signatures (nitrogen /carbon)

Hypothesis 2: difference in isotopic signature between sympatric and allopatric populations (nitrogen)

2 A Differences in mean values between allopatric and sympatric populations (niche shift) 2 B Lower variance in sympatry (niche narrowing)

Niche shift(2 A)

Niche narrowing (2B)

allopatry sympatry

Hypothesis 3: Carbon isotope signature of D.mahan should be higher than the other two species, reflecting the use of resources from marine origin

C3 plants -27‰

seagrasses -10‰

CAM plants -10 to-28‰

C4 plants -12‰

macroalgae -15‰

phytoplankton -22‰ Zooplancton -20‰

Materials and methods The study site

Los Ajaches

Femés

Mña. Blanca

Mña Tinache

B.Co Elv. Sanchez

Catalina Cabr.

La Graciosa Mña. Clara

Sample collection

Locality Habitat DA DN DM Type Total

Bco.Elv.Sanchez s

Mount. 13 (5♂,5♀,3j) 3J)

Allopatry 13

Catalina Cabrera Beach 7(j) Allopatry 7

Femés Mount. 1 (♂) 14 (3♂,4♀,7j) Sympatry 15

La Graciosa Mount. 10 (1♂,4♀,5j) Allopatry 10

Los Ajaches Mount. 4 (1♂,3j) Allopatry 4

Montaña Blanca Mount. 10 (2♂,5♀,3j) 10 (4♂,4♀,2j) Sympatry 20

Montaña Clara Mount. 9 (3♂,5♀,1j) 10 (2♂,5♀,3j) Sympatry 19

Mont. Tinache Mount. 20 (1♂,5♀,14j) 13 (5♂,5♀,3j) Sympatry 33

Total 54 60 7 121

Originally done for other studies (2002-2005)

Isotopic analysis • Measured (prosoma width)

• prosoma and legs for all individuals

• Dried 60 °C

• Homogenized

• Stable isotope analysis with mass spectrometer at Serveis Científico-tècnics de la UB

• δ15N and δ 13C

Statistical analysis

• General lineal models (ANOVA and t-student test)

• Levene test (variance)

Results NAIVE APPROACH

We had results for our hypothesis, but there were biases:

1)Differences in isotopic baseline of localities

2)Sample size too small

3)Heterogeneity of the sample

δ15N

Da Dn Da Dn Da Dn Da Dn Da Dn Da Dn Da Dn Da Dn Da Dn

Factors F-stat p-value

Model 1

SEX 1.76 0.2746

LOC 33.33 0.0084

SEX * LOC 1.85 0.1633

Model 2

SEX 2.74 0.1094

LOC 61.38 <0.0001

PROSOMA WIDTH 0.63 0.4352

Model 3

SEX 2.68 0.1134

LOC 60.79 <0.0001

C:N RATIO 0.29 0.5938

Selected Model

SEX 2.46 0.1280

LOC 64.62 <0.0001

95% CI estimated differences

male-female -0.29 - 2.18

Femés-Tinache 2.47 - 5.76

Mña. Blanca-Tinache 0.30 - 3.59

Mña. Clara-Tinache 9.63 - 13.10

(adults from 4 sympatric localities, n=33)

MODELLING APPROACH: account for parameters related to isotopic values

δ15N in D.nesiotes

PARAMETERS RELATED TO δ 13C in D.nesiotes

Factors F-stat p-value

Model 1

SEX 6.69 0.0761

LOC 3.84 0.1490

SEX * LOC 0.84 0.4853

Model 2

SEX 5.34 0.0287

LOC 3.62 0.0256


Model 3

SEX 2.13 0.1562

LOC 3.92 0.0190

C:N RATIO 4.86 0.0362

Selected Model

LOC 3.38 0.0319

CNRATIO 8.76 0.0062


Femés-Tinache -0.42 - 1.14



1 unit on C:N ratio -4.31 - -0.78

PARAMETERS RELATED TO δ15N and δ 13C in D.alegranzaensis

δ15N F-stat p-value

Model 1

LOC 51.38 <0.0001


Model 2

LOC 39.29 <0.0001

CNRATIO 1.30 0.2783

Selected Model

LOC 41.45 <0.0001




δ13C F-stat p-value

Model 1

LOC 9.69 0.0037

PROSOMA WITDTH 0.00 0.9498

Model 2

LOC 10.52 0.0028

CNRATIO 0.00 0.9850

Selected Model

LOC 13.91 0.0007


Mña. Blanca-Tinache -0.22 - 2.21


Only females from 3 sympatric localities (n=15)

HYPOTHESIS 1 : differences in isotopic mean values between Da and Dn

Adults from 3 sympatric localities

Estimated mean values of δ15N according to species, locality and sex.

For Nitrogen

Model for Hypothesis 1 (nitrogen)

Selected Model

SP 9.09 0.0044

SEX 9.01 0.0046

LOC 140.81 <0.0001


D.alegrazaensis-D.nesiotes 0.56 - 2.83

female-male 0.57 - 2.89



Shift between Da and Dn 0.56-2.83 ‰

Trophic segregation from moderate to high

HYPOTHESIS 1 : differences mean values between DA and DN

Range for C: 4 ‰; for N : 15 ‰

Rather similar carbon signature

For Carbon

2a In mean values –not evaluable 2b In variability ( locality adjusted variance)

HYPOTHESIS 2 : differences between sympatric and allopatric populations

N Locs Condition Inter-individual

variance

Among localities

variance

D. alegrazaensis

Juv. 21 4 Sympatry 8.02 6.13

5 1 Allopatry 44.21 n.e.

♀ 15 3 Sympatry 4.29 34.72

4 3 Allopatry n.e. 0.28

♂ 8 5 Sympatry 0.30 9.49

1 1 Allopatry n.e. n.e.

Adults (♀+♂) 23 5 Sympatry 4.40 15.69

5 3 Allopatry 0.01 0.30

D. nesiotes

Juv. 14 4 Sympatry 2.25 12.52


♀ 18 4 Sympatry 3.34 25.41


♂ 15 4 Sympatry 1.74 22.60

5 1 Allopatry 5.30 n.e.-

Adults (♀+♂) 33 4 Sympatry 3.02 25.20


tested only on N

HYPOTHESIS 3 Use of resources of marine origin in D.mahan

D.Mahan was higher in δ 13C by 7-8 ‰ (2 times the difference among localities)

Tested only on juveniles

Conclusions

We found that Da feeds at a higher trophic level than Dn (clear shift in N) (Hyp 1)

To Compare individuals from different habitats it’s necessasary to calculate the isotopic baseline of each habitat (Hyp 2°a)

Lower variance in some sub-groups of sympatric populations (Hyp 2b).

Dm has a significative higher value of carbon signature, reflecting the use of resources of marine origine (Hyp 3)

Remarkabe differences among localities for nitrogen (not for carbon)

Isotopes inform on trophic level or habitat use, but for the species composition of the diet molecular studies are required

• THANK YOU!

Documents

presentacion Antonio (lluis) (versione definitiva) pdf