De Villiers defence

The dispersal ability, performance
and population structure of Cape
Xenopus frogs

• Xenopus occur throughout sub-Saharan Africa
(Kobel et al., 1981 Picker & De Villiers, 1989; Minter et al., 2004)
• 2 species present in south-western Cape (Kobel et al.,
1981 Picker & De Villiers, 1989; Minter et al., 2004)

• During the winter rains X. laevis move into the
habitat of X. gilli
• X. laevis poses a threat to X. gilli
– Predation
– Competition
– Hybridization
No conservation
for X. gilli
X. gilli conserved
since 1985

• More on the Ecology of Xenopus
• To test the fully aquatic status of Xenopus
• To determine the movement capabilities and
population structure of these two Xenopus
species
• To determine if these two species differ in
these aspects
Aquatic
TerrestrialAquatic

Chap 1 Intro
• Dispersal present in most organisms (Clobert et
al., 2009)
–Not static but differs between and within
species (Altwegg et al., 2000; Schneider et al., 2003; Mennechez et al., 2004;
Bowler & Benton, 2009; Clobert et al., 2009; Stevens et al., 2010)
–Certain cost involved in dispersal (Bowler & Benton,
2005; Clobert et al., 2009)

Dispersal ability
or observed
performance
Lab based
performance
or maximal
performance
Morphology
Chap 1 Intro
Ref: Stevens et al., 2010; Garland & Losos, 1994;
Zug, 1972; Arnold & Bennett, 1984
http://images.natureworldnews.com/data/images/full/2450/cane-toad-in-australia.jpg
Increased Dispersal
Alford et al., 2009
Increased Endurance
Llewelyn et al., 2010
Longer leg length
Phillips et al., 2006

• Amphibians classified as poor dispersers
(Avise, 2000)
–Smith & Green (2005) shown that 44% of
anurans disperse > 1km
–Study only report on single maximum
events
–Study also lacks aquatic anurans
Chap 1 Intro

• Xenopus highly adapted for aquatic
lifestyle(Trueb, 1996)
–Irrigation readily used for dispersal (Tinsley et al., 1996; Lobos
& Measey, 2002; Measey, 2004)
–Overland dispersal documented (see Kalk, 1960; Passmore &
Carrunthers, 1979; Picker, 1985; Schramm, 1987; De Bruyn et al., 1996; Measey & Tinsley, 1998; Fouquet & Measey, 2006; Faraone et
al., 2008)
Chap 1 Intro

Aim:
1. Determine the dispersal ability and the
relative performance
2. Compare dispersal ability and relative
performance
H1: Xenopus laevis will outperform X. gilli
in both dispersal and relative
performance
Chap 1 Intro

• Frogs captured through trapping and seining
• Frogs tagged using PIT tags:
– X. gilli tagged at both sites
– X. laevis tagged only in Kleinmond
Chap 1 Intro M & M

• 20 (10 males & 10 females) X. gilli & X. laevis
collected
• All performance trials done
at 20˚C
• Dry & wet endurance
determined on 4m circular track
• Jumping & swimming speed were determined by
filming the animals at 240fps
• Performance compared using an ANCOVA
Chap 1 Intro M & M

• Literature search to determine which
morphological characters associated with
performance traits
• Log transformed stepwise regression was
done in support of literature
• GLM was used to fit different morphological
characters
• Best model based on Δ AIC
Chap 1 Intro M & M

• Tagged frogs were released in their origin
ponds
• Euclidean distances measured from
origin pond to destination pond
• Distances compared using a MANOVA in
R (R Development Core Team, 2015)
Chap 1 Intro M & M

Ch 1 Intro M & M R & D
CoGH X.gilli Kleinmond X. gilli X. laevis
10
15
20
25
30
35
40
45
50
Relativejumpingdistance(mm)
*
*
CoGH X. gilli Kleinmond X. gilli X. laevis
0
20
40
60
80
100
120
140
160
180
Jumpheight(mm)
*
*

0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Swimspeedm.s-1
*
*
4.0
4.2
4.4
4.6
4.8
5.0
5.2
Log(Wetendurancedistance(mm))
* *
Chap 1 Intro M & M R & D

• Jumping performance related to leg
morphology
– Gomes et al. (2009) & Tejedo et al. (2000) showed
jump distance related to leg length
– Herrel et al. (2012) & Llewelyn et al. (2010)
showed endurance is related to leg length

• Swimming speed related to Illium length and
width in X. gilli
– Supported by Videler and Jorna (1985)
• Swimming endurance related to leg length in
X. gilli
• X. laevis with the longest tibia swam the
fastest but the frogs with the longest bodies
swam the furthest

1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
Log(distance(m))
90 (5.17%)6 (1.01%)46 (4.01%)

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600
0
10
20
30
40
50
200 400 600 800 1000 1200 1400 1600 1800
0
10
20
30
40
50
Frequency
Distance (m)
1560m within 3 weeks

Ch 1 Intro M & M R & D
0
5
10
15
20
25
30
35
40
Feb
'14
Mar
'14
Apr
'14
May
'14
Jun
'14
Jul
'14
Aug
'14
Sep
'14
Oct
'14
Nov
'14
Dec
'14
Jan
'15
Feb
'15
Mar
'15
Apr
'15
May
'15
Jun
'15
Jul
'15
Aug
'15
Sep
'15
Oct
'15
Frequency

Chap 1 Intro M & M R & D Chap 2

• Population structure important method to
monitor amphibian populations (Leberton et al., 1992;
Schmidt, 2003)
– Important for assessment of IUCN status (see IUCN,
2012)
– No data on population structure of SA frogs (see
Measey, 2011; IUCN 2012)
Chap 1 Intro M & M R & D Chap 2 Intro

Frequency
Age
Age
Frequency
NumberofSurvivors
Age
Survival
Survival
Age

• X. laevis has a suggested negative effect
X. gilli
• CoGH and Kleinmond different
conservation histories
– Opportunity to determine if X. laevis has a
negative affect on X. gilli

Aim
1. Obtain information on the age
structure, growth and survival
2. Determine whether X. laevis has a
negative effect on X. gilli
H1: The presence of Xenopus laevis has a
negative effect on the survival as well as
the age structure of Xenopus gilli

• Outer toe from 40 frogs (20 males & 20 Females)
of each species from each site
• Each toe was sectioned
and stained using
standard
skeletochronological
techniques
• The relationship between
number of LAG and SVL
was determined using
non-linear regression
(R Core team, 2015)
Chap 1 Intro M & M R & D Chap 2 Intro M & M

• All frogs that were captured were sexed and
photographed
– If a frog was recapture it was photographed again
• The difference in SVL was determined and
growth expressed as Growth/day
• Relationship between growth and initial SVL
was expressed by a non-linear regression (R Core
team, 2015)
Chap 1 Intro M & M R & D Chap 2 Intro M & M ImageJ

• Frogs were captured on 3 consecutive days
every 3 to 6 weeks
– Recapture events were recorded in binary (1 & 0)
• CJS model was used to determine the survival
of the frogs
Chap 1 Intro M & M R & D Chap 2 Intro M & M
20 30 40 50 60 70 80 90 100 110 120 130 140
0
100
200
300
400
500
600
20 25 30 35 40 45 50 55 60 65 70 75
0
100
200
300
400
500
600
Small Large Small Large

Chap 1 Intro M & M R & D Chap 2 Intro M & M R & D
0 1 2 3 4 5 6 7 8 9 10
20
30
40
50
60
70
80
90
100
110
120
0 1 2 3 4 5 6 7 8
25
30
35
40
45
50
55
60
65
0 2 4 6 8 10
30
40
50
60
70
80
90
100
110
120
0 1 2 3 4 5 6 7 8
38
40
42
44
46
48
50
52
54
56
58
60
62
64
66
SVL
Age (years)
0
50
100
150
200
250
15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 65-70 70-75 75-80Frequency
Cape of Good Hope
0
50
100
150
200
250
15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 65-70 70-75 75-80
Frequency
SVL classes (mm)
Kleinmond

-0.02 -0.01 0.00 0.01 0.02 0.03 0.04
30
35
40
45
50
55
60
65
70
75
-0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12
30
35
40
45
50
55
60
65
70
-0.12 -0.08 -0.04 0.00 0.04 0.08 0.12 0.16
30
40
50
60
70
80
90
100
110
120
130
SVL
Growth/day

0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Summer '14 Winter'14 Summer '14/'15 Winter '15 Summer '15
Survival
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Survival
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Survival
X. laevis: 0.381
Kleinmond: 0.316
CoGH: 0.562

• Xenopus are principally aquatic rather than
fully aqautic
• X. laevis better jumper and swimmer
• X. laevis higher dispersal frequency
• Skeletochronology not effective in age
determination of Cape Xenopus
• Survival is reduced in Kleinmond X. gilli

• Kleinmond
– Origin of X. laevis in temp ponds
– Aestivation place of X. gilli
• CoGH
– Breeding sites of X. gilli
– Fate of X. gilli after the ponds dry up

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