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The island syndrome describes the evolution of slow life history traits in insular environments. Animals are thought to evolve smaller clutches of larger offspring on islands in response to release from predation pressure and interspecific competition, and the resulting increases in population density and intraspecific competition. These forces become more pronounced with diminishing island size, and life histories are thus expected to become slowest on small, isolated islands. We measured clutch sizes in 12 insular populations of Mediodactylus kotschyi, a small gecko from the Cyclades Archipelago, a set of land-bridge islands in the Aegean Sea (Greece). We analyse variation in clutch size in relation to island area, island age, maternal body size, the presence of putative competitors and nesting seabirds (which increase resource abundance in the form of marine subsidies), and richness of predators. Clutch size of M. kotschyi decreases with increasing island area, in departure from classic island syndrome predictions, sug-gesting the evolution of faster life histories on smaller islands. There are no relationships between clutch size and island age, maternal size, the presence of competitors or predator richness. Instead, larger clutches on small islands could simply reflect the beneficial effect of marine subsidies derived from resident seabird colonies. Indeed, populations of M. kotschyi on islands with nesting seabirds have clutch sizes 30.9 % larger (1.82 vs. 1.39 eggs) than populations on islands without nesting seabirds. Thus, our data suggest that bottom-up effects of marine subsidies may supersede the expression of a simple island syndrome in the Aegean M. kotschyi.
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Clutch Size Variability in an Ostensibly Fix-Clutched Lizard:
Effects of Insularity on a Mediterranean Gecko
Alex Slavenko Yuval Itescu Johannes Foufopoulos
Panayiotis Pafilis Shai Meiri
Received: 16 October 2014 / Accepted: 5 January 2015
ÓSpringer Science+Business Media New York 2015
Abstract The island syndrome describes the evolution of
slow life history traits in insular environments. Animals are
thought to evolve smaller clutches of larger offspring on
islands in response to release from predation pressure and
interspecific competition, and the resulting increases in
population density and intraspecific competition. These
forces become more pronounced with diminishing island
size, and life histories are thus expected to become slowest
on small, isolated islands. We measured clutch sizes in 12
insular populations of Mediodactylus kotschyi, a small
gecko from the Cyclades Archipelago, a set of land-bridge
islands in the Aegean Sea (Greece). We analyse variation
in clutch size in relation to island area, island age, maternal
body size, the presence of putative competitors and nesting
seabirds (which increase resource abundance in the form of
marine subsidies), and richness of predators. Clutch size of
M.kotschyi decreases with increasing island area, in
departure from classic island syndrome predictions, sug-
gesting the evolution of faster life histories on smaller
islands. There are no relationships between clutch size and
island age, maternal size, the presence of competitors or
predator richness. Instead, larger clutches on small islands
could simply reflect the beneficial effect of marine
subsidies derived from resident seabird colonies. Indeed,
populations of M. kotschyi on islands with nesting seabirds
have clutch sizes 30.9 % larger (1.82 vs. 1.39 eggs) than
populations on islands without nesting seabirds. Thus, our
data suggest that bottom-up effects of marine subsidies
may supersede the expression of a simple island syndrome
in the Aegean M. kotschyi.
Keywords Cyclades Island biogeography Island
syndrome Kotschyi’s gecko Life history Reproduction
Mediodactylus kotschyi
The evolution of life histories on islands has received much
attention in the past two decades (e.g., Adler and Levins
1994; Adler 1996; Adamopoulou and Valakos 2000; Knapp
et al. 2006; Salvador and Fernandez 2008; Raia et al. 2010;
Pafilis et al. 2011; Novosolov and Meiri 2013; Novosolov
et al. 2013). The life history of animals is defined by a wide
set of traits associated with the timing and magnitude of
reproductive and ontogenetic events (Stearns 1992). Much
research has focused on the concept of life history strategies
that describe the concerted evolution of various life history
traits, originally conceived as rand Kstrategies (MacArthur
and Wilson 1967; Pianka 1970). This theory generally dis-
tinguished between organisms that mature early and produce
many small offspring (r-selected) and organisms that mature
late and produce few large offspring (K-selected). The two
strategies were traditionally interpreted as the outcome of
density-dependent (at carrying capacity, K) or density-
independent population growth (selected for a high intrinsic
rate of increase, r). Lack of empirical findings to support this
theory (see e.g., Stearns 1992; Reznick et al. 2002) has
A. Slavenko (&)Y. Itescu S. Meiri
Department of Zoology, Tel Aviv University, 6997801 Tel Aviv,
J. Foufopoulos
School of Natural Resources and the Environment, University of
Michigan, Ann Arbor, MI, USA
P. Pafilis
Department of Zoology and Marine Biology, School of Biology,
University of Athens, Panepistimioupolis, Ilissia, Greece
Evol Biol
DOI 10.1007/s11692-015-9304-0
caused it to lose stature and the emphasis now lies with the
covariations of life history traits on a ‘‘fast-slow’’ continuum
(with ‘‘fast’’ life history similar to rstrategy and ‘‘slow’’ life
history similar to Kstrategy) in response to selection pres-
sures acting on age-specific mortality rates (Stearns 1983;
Read and Harvey 1989; Promislow and Harvey 1990;
Stearns 1992; Reznick et al. 2002; Bielby et al. 2007).
Adler and Levins (1994) showed that insular rodent
populations tend to have denser, more stable populations,
larger body sizes, delayed maturity, smaller litters and
larger offspring. They suggested that, according to this
pattern, which they termed ‘‘the island syndrome’’,
increasing population density and changes in mortality
rates due to lack of predators and interspecific competitors
on islands (MacArthur et al. 1972), lead to selection for
slower life histories (Adler and Levins 1994).
The physical and ecological characteristics of the islands
are expected to affect the extent to which changes pre-
dicted by the island syndrome are expressed. As isolation
increases (i.e., geographical distance from the mainland),
islands are expected to become increasingly species-poor
(MacArthur and Wilson 1967), and consequently poorer in
predators and competitors. Adler and Levins (1994)
therefore predicted that the expression of the island syn-
drome will be stronger on more isolated islands, as popu-
lation density is expected to be highest there. Conversely,
expressions of the island syndrome are expected to
decrease with increasing island area (Adler and Levins
1994). As islands grow larger, they become more ‘main-
land-like’ (Whittaker and Ferna
´ndez-Palacios 2007), and
therefore contain more species, more available niches, and
more competitors and predators, cancelling out the effects
of insularity (but see Meiri et al. 2005).
Support has been found for the island syndrome in
mammals (e.g., Adler and Levins 1994; Adler 1996; Gol-
tsman et al. 2005), birds (e.g., Covas 2012), amphibians
(e.g., Wang et al. 2009), snakes (Tanaka and Mori 2010;
´et al. 2013), and lizards (e.g., Adamopoulou and
Valakos 2000; Novosolov and Meiri 2013; Novosolov
et al. 2013). However, most of these studies either com-
pared island-endemic species to mainland congeners (e.g.,
Adamopoulou and Valakos 2000), or compared a single
insular population to a mainland population (e.g., Tanaka
and Mori 2010). As such, they offer little insight on the
effects of island area and insularity on evolution of life
history traits. Novosolov et al. (2013) found that island
endemic lizards have smaller clutches of larger hatchlings,
but no effect of island area on the life history traits they
A few intraspecific studies have also identified insular
populations that appear to depart in their life history traits
from the predictions of the island syndrome. Raia et al.
(2010) found that an insular population of the Italian wall
lizard, Podarcis sicula, displayed a ‘‘reversed island syn-
drome’’, i.e., higher aggressiveness and a greater repro-
ductive effort, where population densities were low or
fluctuating due to environmental unpredictability (see also
Monti et al. 2013). When studying Podarcis gaigeae,a
wall lizard species endemic to the Skyros archipelago in
the Aegean Sea, Pafilis et al. (2011) found that populations
on smaller islands exhibited a higher reproductive effort,
with no visible trade-offs between egg size and clutch size.
Furthermore, the authors found that the differences in life
history traits between populations were explained by
maternal body size, i.e., the lizards on small islands grow
larger, with proportional increases in clutch and egg sizes.
One of the main drivers responsible for this counter-intu-
itive response to insularity is likely the elevated resource
abundance resulting from ‘‘marine subsidies’’ (i.e., nutri-
ents imported by seabirds from the surrounding marine
ecosystems in the form of food scraps, carcasses and
guano; see Anderson and Polis 1998). Such subsidies can
have profound effects on insular lizard ecological and
physiological traits and population densities (Sa
˜ero and Polis 2000; Barrett et al. 2005; Pafilis et al.
2009b), and highlight how high food availability can
release species from life history trade-offs (Pafilis et al.
2011). If so, the exact interaction between island charac-
teristics and life history traits still has room for exploration.
Mediodactylus kotschyi (Kotschy’s gecko) is a small
(snout-vent length up to 56 mm; Valakos and Vlachopanos
1989; and mass up to 5.5 g; our unpublished data), cathe-
meral, mainly insectivorous (Valakos and Polymeni 1990)
gecko, highly abundant on the Aegean Sea islands,
including extremely small islets (Valakos et al. 2008; and
our pers. obs.). Insular populations of M. kotschyi have
persisted since the islands were separated from the main-
land as sea levels rose following the end of the Last Glacial
Maximum (Kasapidis et al. 2005). These geckos show
large morphological and life history variability across
islands (Valakos et al. 2008; and our pers. obs.).
The reproductive biology of the species has been mod-
estly studied: M. kotschyi has a fairly constant clutch size
of one, two or three eggs, similar to other geckos (Kluge
1987; Goldberg 2012), but differences in mean clutch size
between populations can still be discerned (Goldberg
2012), and egg volume is variable (Mollov 2011). While
such studies give insight into the general reproductive
biology of the species, we still lack comparative research at
the population level, particularly on islands.
In this study, we examined clutch sizes of insular pop-
ulations of M. kotschyi from different islands of varying
size in the Cyclades archipelago, Greece. We predicted
that, according to the island syndrome, clutch size of M.
kotschyi would decrease with decreasing island area and
increasing island age, the geckos having adopted a slower
Evol Biol
life history on small, isolated islands with few predators
and competitors. We further explicitly tested predictions
arising from the proposed causal mechanism of the island
syndrome, i.e., the effects of release from predation pres-
sure and interspecific competition, as well as effects of
resource abundance on life history traits. We examined if
clutch size of M. kotschyi increased with decreasing rich-
ness of predators and competitors, and with increasing
resource abundance, using the presence of seabird nesting
colonies, which deliver marine subsidies, as a proxy.
During May and June 2014,we surveyed 17 islands of varying
sizes in the Cyclades archipelago, Greece. We searchedfor M.
kotschyi on the ground or dry stone walls, and under rocks and
other items. All geckos were captured by hand.
Upon capture, we measured snout-vent length (SVL)
and mass, and determined sex by visual examination of the
cloacal region (Beutler and Gruber 1979). For female
geckos, we determined whether they were gravid, and
measured clutch size, by palpation of the abdomen and
visual examination. This is possible thanks to their semi-
transparent colouration, which makes the eggs readily
visible in this species (Fig. 1). After measuring the ani-
mals, we released them back into the wild, apart from a few
specimens that were captured and transferred to a housing
facility in the University of Athens for further research.
We calculated island areas using Google Maps. Times
of separation of islands in the Aegean Sea have previously
been estimated using bathymetric maps and charts that give
the rates of sea level change (Foufopoulos and Ives 1998,
1999). We used updated times of separation for the 17
surveyed islands to construct a dendrogram of the island
separation (Fig. 2) and to calculate island age as a proxy
for isolation, hereby considered as the time since separation
from a larger landmass. The dendrogram was used for the
phylogenetic analysis of the studied populations, in order to
control for a phylogenetic signal in clutch size, under the
assumption that the main mode of divergence of popula-
tions of M. kotschyi in the Cyclades is vicariance. This
seems a reasonable assumption, as the timing of divergence
of populations of M. kotschyi closely correlates with the
timing of geological events related to the formation of
islands and island clusters in the Aegean (Kasapidis et al.
2005). Furthermore, M. kotschyi seem to be poor dispersers
(Scillitani et al. 2004), likely limiting gene flow between
insular populations.
In order to account for the possible effects of maternal
body size on clutch size (Meiri et al. 2012), we examined
the effect of mean SVL on mean clutch size. We used SVL
and not mass as our proxy for maternal body size due to the
fact that clutch size and maternal mass are not statistically
independent, because the clutch constitutes a relatively
large fraction of a gravid female’s body mass. We used
log-transformed values of mean SVL, island area and
island age as predictors, in order to linearize the relation-
ship, normalise residuals, and reduce heteroscedasticity.
We used literature data (Valakos et al. 2008; Pafilis et al.
2009a, and references within; Brock et al. 2014), and our
own observations from the field, to derive proxies for
predation pressure, interspecific competition, and marine
subsidies. The pooled number of potential avian (Buteo
buteo,B. rufinus,Circaetus gallicus,Falco tinnunculus,F.
eleonorae,Athene noctua,Lanus senator,Corvus corax
and C. corone), mammalian (domestic cats, Martes foina,
Rattus norvegicus, and R. rattus), and reptilian predators
(Dolichophis caspius,Elaphe quatuorlineata,Eryx jaculus,
Macrovipera schweizeri,Natrix natrix,N. tessellata,
Platyceps najadum,Telescopus fallax,Vipera ammodytes,
and Zamenis situlus) present on each island was our proxy
for predation pressure (Table 1). As a proxy for interspe-
cific competition, we used the presence of Hemidactylus
turcicus, a similar-sized, insectivorous gecko, and the only
other gecko species present on the Cyclades (Valakos et al.
2008). These two species are found on many of the same
islands, and often their densities display inverse relation-
ships, i.e., where one is abundant the other is not (Foufo-
poulos 1997). We used presence of nesting seabirds
(mainly Larus michahellis) as a proxy for marine subsidies,
as these gulls provide nutrients from marine ecosystems
that indirectly enrich the arthropod fauna on islands
(Anderson and Polis 1999;Sa
˜ero and Polis
2000), the main food resource for M. kotschyi (Valakos and
Polymeni 1990).
Sample sizes from the islands were unequal (Table 1).
We therefore omitted five islands, from which we had
extremely low clutch sample sizes (although we still report
them; Table 1), and divide the remaining data into two
subsets, to control for data quality due to unequal
Fig. 1 A gravid female M. kotschyi from Venetiko Isl., Greece.
Encircled are two eggs, clearly visible in the abdomen
Evol Biol
sampling: (A) a subset of 12 islands where we sampled
three or more geckos; and (B) a subset of nine islands
where we sampled five or more geckos.
We performed a phylogenetic generalised least square
(PGLS) regression (Freckleton et al. 2002) using the ‘caper’
package in R (Orme et al. 2012) to estimate the maximum
likelihood value of the scaling parameter k, and conducted
two analyses. In one, we examined the effects of island traits
(area and age) and maternal body size (SVL) on clutch size
in M. kotschyi to determine the insular patterns in this spe-
cies’ clutch size. In the second analysis, we used the pre-
sence of H. turcicus (yes/no), the presence of nesting
seabirds (yes/no), and predator species richness as predic-
tors, to examine the effects of interspecific competition,
resource abundance, and predation pressure (possible causal
mechanisms) on the same trait. Model selection was based
on pvalues. All statistical analyses were performed in R
v3.1.1 (R Development Core Team 2013) using the RStudio
v0.98.978 interface (RStudio Inc. 2013).
Clutch size of M. kotschyi varied between one and three
eggs, and island means varied between one and 2.2 eggs,
with an overall mean value of 1.5 (Table 1). These are
smaller clutches than were previously reported for this
species from the Aegean islands (1.86 eggs; Goldberg,
2012). We found no correlation, in either subset [i.e., A
(n =12) and B (n =9)], between mean clutch size and
either mean SVL or island age. There is no phylogenetic
signal in the relationship between clutch size and any of the
predictors (k=0 in both subsets), i.e., closely related
populations do not have similar clutch sizes. Mean clutch
size was likewise unaffected by either the presence of H.
turcicus or by predator richness.
In subset A, mean clutch size decreases with increasing
island area (slope =-0.06 ±0.03
p=0.047; Fig. 3). This model explains 37 % of the var-
iation in mean clutch size across populations of M. kots-
chyi. This correlation is similar, but even stronger in subset
B, with an even steeper slope (slope =-0.09 ±0.03
=10.17, p=0.019; Fig. 3). This model explains
63 % of the variation.
In subset B, mean clutch size is 30.9 % higher for
islands with nesting seabirds (1.82 vs. 1.39 for islands with
and without nesting seabirds, respectively; F
p=0.026, R
=0.59; Fig. 4). However, presence of
nesting seabirds is not correlated with mean clutch size in
the less conservative subset A.
Greece Tur key
Fig. 2 Map of the 17 surveyed islands (red) in the Cyclades archipelago, Greece, along with a dendrogram showing times of separation. The
map was generated in ArcGIS 10.0 (ESRI 2010), using a National Geographic Society basemap (ESRI 2014) (Color figure online)
Evol Biol
Mean clutch size of insular populations of M. kotschyi
decreases with increasing island area. This correlation is
evident in our liberal dataset A, and becomes even stronger
in the smaller, more conservative B dataset, explaining
more than half of the variation in gecko clutch size in that
subset, despite the reduction in the sample size of analysed
Decreasing clutch size with increasing island area is the
opposite of what we predicted, and could be viewed as
suggestive of faster life histories on smaller islands, i.e., a
reverse island syndrome (Raia et al. 2010). There is also
some evidence that the geckos from Naxos island in the
Cyclades Archipelago, Greece have smaller egg volumes
than geckos from mainland Europe (Mollov 2011) and
Israel (Werner 1993), again suggestive of faster life his-
tories in insular populations. Faster life histories are pre-
dicted to evolve in insular environments under low or
fluctuating population densities (Raia et al. 2010). How-
ever, M. kotschyi populations are both highly abundant and
appear overall stable on small Cycladic islands (pers. obs.).
Furthermore, M. kotschyi from a mainland population in
Bulgaria have mean clutch sizes of 2.25 eggs (Mollov
2011), larger than all mean clutch sizes in our dataset
(Table 1). This is similar to the findings of another study
held at Naxos, the largest island in the Cyclades (Valakos
and Vlachopanos 1989; we have just one datum from
Naxos, of a two-egg clutch). These data make difficult the
claim that geckos on Cycladic islands have faster life his-
tories than mainland populations. Therefore, while our
results seem to correspond to at least some of the predic-
tions of the reverse island syndrome (Raia et al. 2010), we
still lack concrete data on life history traits of mainland
populations of M. kotschyi and insular and mainland pop-
ulation densities to explicitly test the syndrome.
The observed negative correlation between island area
and cutch size does not imply a causal mechanism in
shaping the clutch size of geckos. Island area most often
shapes a species’ life history through its effects on the
diversity of predators and competitors. Surprisingly, we
found no correlation between clutch sizes of M. kotschyi
and either the presence of H. turcicus or predator richness,
despite both being tightly correlated with island area
(Foufopoulos et al. 2011). While this possibly suggests lack
of support in our system for these particular causal mech-
anisms of the island syndrome, it is also possible that the
presence of H. turcicus and predator richness are simply
not reliable proxies for interspecific competition and pre-
dation pressure on M. kotschyi (Meiri et al. 2014).
While H. turcicus can frequently be found co-occurring
in the same microhabitat patches (e.g., under the same
rocks in Greece, or on the same trees in Israel; pers. obs.) it
is significantly more nocturnal than M. kotschyi (Valakos
Table 1 Mean clutch sizes of M. kotschyi from 17 different islands in
the Cyclades archipelago, Greece, along with island area, island age
(regarded as time since separation from larger landmass), geographic
coordinates, and data on predator richness (bbirds, mmammals,
ssnakes), presence of Hemidactylus turcicus, and presence of nesting
Island Mean clutch
Island area
Island age
# of predator
(datum: WGS84)
Anafi 1.33 9 38.64 1,800,000 2 (b, m) Yes No 36.3627°N, 25.7689°E
Aspronisi 2 11 0.04 5,450 2 (b, m) Yes Yes 36.8553°N, 25.5461°E
Glaronisi 2.2 5 0.19 5,600 2 (b, m) No Yes 36.9165°N, 25.6048°E
Ios 1 8 108.71 11,750 3 (b, m, s) Yes No 36.7262°N, 25.3255°E
Iraklia 1.67 6 18.12 9,800 3 (b, m, s) Yes No 36.8412°N, 25.4546°E
Kitriani 1.33 3 0.75 7,700 1 (m) No Yes 36.9050°N, 24.7265°E
Kopria 1.33 3 0.14 11,700 2 (b, m) No Yes 36.9858°N, 25.6387°E
Kythnos 1.4 10 99.42 1,800,000 3 (b, m, s) Yes No 37.4034°N, 24.4288°E
Megalo Fteno 1.67 6 0.07 9,650 1 (b) No Yes 36.3111°N, 25.7999°E
Mikro Fteno 1 1 0.03 9,650 1 (b) No Yes 36.3116°N, 25.7954°E
Naxos 2 1 430.17 8,700 3 (b, m, s) Yes No 37.0551°N, 25.4526°E
Pacheia 2 2 1.41 12,250 2 (b, m) No No 36.2727°N, 25.8317°E
Schinoussa 1.5 2 8.13 9,550 3 (b, m, s) Yes No 36.8718°N, 25.5202°E
Serifos 1.33 3 74.09 1,800,000 3 (b, m, s) Yes No 37.1543°N, 24.4851°E
Sifnos 1 1 77.38 1,800,000 3 (b, m, s) Yes No 36.9674°N, 24.7041°E
Sikinos 1.57 7 41.23 11,650 3 (b, m, s) Yes No 36.6805°N, 25.1202°E
Venetiko 1.4 10 0.19 9,550 2 (b, m) No Yes 36.8560°N, 25.4849°E
Evol Biol
et al. 2008; and our pers. obs.). Therefore, it is possible that
H. turcicus does not exert strong enough competitive
pressure to induce selection on life history traits in M.
kotschyi. Likewise, although predator richness has often
been used as a proxy for predation pressure (e.g., Brock
et al. 2014), it may be an inadequate index in the case of M.
kotschyi, as other factors such as individual predator for-
aging tactics, population density and activity time may
more strongly shape predation pressure.
Clutch sizes are significantly larger on islands with
nesting seabirds, all of which are small (with an area of
; Table 1). This relationship, coupled with the
failure of either presence of competitors or predator rich-
ness to explain variation in clutch sizes of M. kotschyi,
suggests that clutch sizes of geckos may be linked to
resource abundance. Nesting seabirds provide marine
subsidies—nutrients from marine ecosystems (Anderson
and Polis 1998). Cycladic islands are in general both
nutrient poor and unproductive, though many small islands
in the Cyclades support important nesting seabird colonies
(e.g., Phalacrocorax aristotelis, Calonectris diomedea,
Puffinus yelkouan, Larus michahellis and L. audouinii; Fric
et al. 2012). Breeding colonies of the yellow-legged gull
(Larus michahellis) can be particularly substantial (e.g.,
exceeding densities of 26 breeding pairs/ha on Aspronisi;
pers. obs.) and strongly shape the food webs on these islets
(Mulder 2011; Fric et al. 2012). It is unclear whether these
gulls actually prey on reptiles (Pe
´rez-Mellado et al. 2014).
We have observed no attempts at such predation, and liz-
ards (including the strictly diurnal, highly active Podarcis
erhardii) occur in the immediate vicinity of nests but never
seem nervous or vigilant around the birds. The influx of
marine-derived nutrients, however, has been shown to
greatly affect reptile life history in the Aegean (Pafilis et al.
2009b). In fact, earlier research revealed that marine sub-
sidies were associated with a reversal of the island syn-
drome and dramatic increases in reproductive output
(clutch size: 43.3 %, clutch volume: 107 %) in the Aegean
lizard P. gaigeae (Pafilis et al. 2011). While seabirds only
nest on Cycladic islands during the spring and early sum-
mer (Fric et al. 2012) most species are present throughout
the year and thus provide a steady source of nutrient inputs
for the island food webs. Productivity of islet ecosystems is
tied to seasonal precipitation patterns and thus varies
strongly with the time of the year. Nonetheless this varia-
tion is highly predictable, with little apparent inter-annual
variability (pers. obs.) and as such seems unlikely to satisfy
the requirements for the evolution of the reverse island
syndrome (Raia et al. 2010; Monti et al. 2013). As such,
more data are needed to elucidate the conditions for reverse
island syndrome evolution.
Mediodactylus kotschyi from Greek islands are known
to produce multiple clutches per year (Goldberg 2012), and
a shift to slower life histories in insular environments could
also result in the laying of fewer clutches per year (Nov-
osolov and Meiri 2013) rather than decreased clutch sizes.
Such a case could potentially lead to our observed pattern
(e.g., if the small clutches on larger islands may represent a
second, smaller clutch, following an early large clutch that
leaves females depleted, or clutch size may simply be
compensated for by frequent laying). At the moment,
however, the exact interplay between clutch size and brood
frequency in this species remains difficult to unravel.
The island syndrome, which was originally observed in
mammals (Adler and Levins 1994), has been widely
studied in lizards in recent years (e.g., Raia et al. 2010;
Pafilis et al. 2011; Monti et al. 2013; Novosolov et al.
2013), and results occasionally fail to fully support the
predicted pattern, sometimes even finding evidence for a
reverse trend. On the surface, our results may appear like
they contradict the classical expression of the island syn-
drome and rather support the reverse pattern. A more
Fig. 3 Linear regression of mean clutch size of M. kotschyi against
island area (km
; log-transformed). White dots and dashed line
represent subset B (islands with a sample size of five or more
clutches); white and black dots together and continuous line represent
subset A (islands with a sample size of three or more clutches).
Islands on the left part of the graph (area \1km
) harbor seabird
Fig. 4 Mean clutch size of M. kotschyi on islands with and without
nesting seabirds (subset B: islands with sample size of five or more
clutches, n =9)
Evol Biol
thorough analysis instead suggests that the presence of
marine subsidies, which are restricted to small islets
in area), may simply mask any expression of the
island syndrome. Because of a relatively small sample size,
we are not able to statistically disentangle island area
effects from the presence of marine subsidies, and deter-
mine if a relaxation in life history constraints due to
resource abundance, or selection for faster life histories
following inconstant and unpredictable food supplies is
responsible for the observed patterns. Our data, however,
indicate that that life history traits of island lizards are
subject to various selection pressures, and cannot be simply
predicted by a straight-forward, directional response to
The land-bridge islands of the Cyclades constitute an
interesting study system, with an abundant and diverse
fauna and flora that allow for a detailed examination of the
effects of insularity on evolution (Hurston et al. 2009). M.
kotschyi, despite having a relatively fixed clutch size, still
displays variation in this trait, and even an unexpected
relationship with island area. Further research on other life
history traits of these geckos (e.g., brood frequency or egg
volume), or on similarly abundant animals with larger
variation in clutch size (e.g., P. erhardii), could shed
considerable light on the causative mechanisms behind life
history evolution on islands.
Acknowledgments We thank Nir Enav, Gaya Savyon, Stav Brown,
Shani Levinkind, Amir Lewin, Maayan Mania and Rachel Schwarz
for their invaluable help in the field. This study was supported by the
Israel Science Foundation (Grant No. 1005/12, to Shai Meiri). All
animals were captured under Permit No. 111165/1558 issued by the
Directorate of Forests, National Parks and Hunting, Ministry of
Environment, Energy and Climate Change.
Conflict of interest The authors declare that they have no conflict
of interest.
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... Huang, 2007;Novosolov, Raia, & Meiri, 2013;Pafilis et al., 2011;Siliceo & Diaz, 2010;Slavenko, Itescu, Foufopoulos, Pafilis, & Meiri, 2015), forested habitats (e.g. Werneck, Giugliano, Colleavtti, & Colli, 2009), and saxicolous and arboreal habits (Mesquita et al., 2016;Schall, 1983;Vitt, 1981).Few studies have addressed adaptive responses in reptile clutch size to global variation in climate. ...
... We designate all members of the Gekkota, Dactyloidae, Alopoglossidae, and Gymnophthalmidae as having fixed clutches even though clutch sizes of three or more eggs have been reported for a few of them. For example, the gecko Mediodactylus kotschyi sometimes lays three eggs, although clutches of one or two eggs are much more common (Goldberg, 2012;Slavenko et al., 2015); nonetheless, we treated it as a fixed-clutch species. Species belonging to all other taxa were treated as having variable clutch sizes. ...
Aim Clutch size is a key life‐history trait. In lizards, it ranges over two orders of magnitude. The global drivers of spatial and phylogenetic variation in clutch have been extensively studied in birds, but such tests in other organisms are lacking. To test the generality of latitudinal gradients in clutch size, and their putative drivers, we present the first global‐scale analysis of clutch sizes across lizard taxa. Location Global. Time period Recent. Major taxa studied Lizards (Reptilia, Squamata, Sauria). Methods We analysed clutch‐size data for over 3,900 lizard species, using phylogenetic generalized least‐square regression to study the relationships between clutch sizes and environmental (temperature, precipitation, seasonality, primary productivity, insularity) and ecological factors (body mass, insularity, activity times, and microhabitat use). Results Larger clutches are laid at higher latitudes and in more productive and seasonal environments. Insular taxa lay smaller clutches on average. Temperature and precipitation per se are unrelated to clutch sizes. In Africa, patterns differ from those on other continents. Lineages laying small fixed clutches are restricted to low latitudes. Main conclusions We suggest that the constraint imposed by a short activity season, coupled with abundant resources, is the main driver of large‐clutch evolution at high latitudes and in highly seasonal regions. We hypothesize that such conditions – which are unsuitable for species constrained to laying multiple small clutches – may limit the distribution of fixed‐clutch taxa.
... Shedding light on details about lizards with invariant clutch size, intra-specific variation in clutch size have been reported in several gecko species, including Gekko japonicus (Zhang et al., 2016), Gymnodactylus amarali (Colli et al., 2003), Heteronotia binoei (Kearney and Shine, 2005), Lepidodactylus lugubris (Brown and Sakai, 1988), Mediodactylus kotschyi (Slavenko et al., 2015), Paroedura picta (Kubička and Kratochvíl, 2009), and Ptyodactylus guttatus (Johnston and Bouskila, 2007). These geckos usually produce double-egg but occasionally lay single-egg, which means that clutch size of geckos is not strictly fixed. ...
... The occasional single-egg clutch was ascribed to adaptive control of the reproductive output (Colli et al., 2003) or reproductive failure like accidental disappearance and absorption of one of two eggs (Kubička and Kratochvíl, 2009). From another point of view, intra-specific variation in gecko clutch size was explained by geographic factors, such as insularity or island syndrome (Slavenko et al., 2015;Schwarz and Meiri, 2017). However, a detailed comparison between single-and double-egg clutches has been reported in only a few gecko species (e.g., G. amarali, M. kotschyi, and P. picta); therefore, we still lack the interpretation of clutch size variation within gecko species. ...
Although the majority of reptiles show variable clutch sizes, geckos have a fixed clutch size (one or two eggs) and modify reproductive output by changing the offspring size or clutch frequency. However, the clutch size of several geckos is not strictly fixed at the species level; they actually lay both single- and double-egg clutches. We still do not fully understand if clutch size variation within a gecko species is due to adaptive control or reproductive failure like accidental absorption of one of two eggs. This study investigated differences between single- and double-egg clutches of a gecko species in terms of reproductive frequency, egg size, and offspring trait. I housed mourning geckos Lepidodactylus lugubris in a controlled environment and observed their reproduction for seven years. No large differences between single- and double-egg clutches were detected in reproductive frequency and egg size, indicating that life-history trade-offs do not explain much about clutch size variation. Single-egg was comparable in egg size to double-egg, but hatchlings from single-egg showed significantly lower body condition than did those from double-egg. These results suggest that the single-egg is not only a reduction of reproductive output per clutch, but it may provide negative effect on ontogeny.
... Specifically, island populations are predicted to contain individuals that are larger, less aggressive, live at higher densities, and shift their reproductive strategies to produce fewer, larger offspring (Halpin and Sullivan 1978;Adler and Levins 1994;Goltsman et al. 2006). Both the 'island syndrome' and 'island rule' have been examined in a variety of taxa including mammals (e.g., Michaux et al. 2002;Lister and Hall 2014), reptiles (e.g., Novosolov et al. 2012;Novosolov and Meiri 2013;Slavenko et al. 2015) and birds (e.g., Wang et al. 2009;Covas 2012;Ramos 2014). Furthermore, several large-scale meta-analyses have been undertaken to examine the generality of such phenotypic changes and what environmental or ecological factors underlie them (Benítez-López et al. 2021;Meiri et al. 2005Meiri et al. , 2008Raia and Meiri 2006;Lomolino et al. 2011Lomolino et al. , 2013. ...
The island syndrome hypothesis (ISH) stipulates that, as a result of local selection pressures and restricted gene flow, individuals from island populations should differ from individuals within mainland populations. Specifically, island populations are predicted to contain individuals that are larger, less aggressive, more sociable, and that invest more in their offspring. To date, tests of the ISH have mainly compared oceanic islands to continental sites, and rarely smaller spatial scales such as inland watersheds. Here, using a novel set of genome-wide SNP markers in wild deer mice (Peromyscus maniculatus) we conducted a genomic assessment of predictions underlying the ISH in an inland riverine island system: analysing island-mainland population structure, and quantifying heritability of phenotypes thought to underlie the ISH. We found clear genomic differentiation between the island and mainland populations and moderate to high marker-based heritability estimates for overall variation in traits previously found to differ in line with the ISH between mainland and island locations. FST outlier analyses highlighted 12 loci associated with differentiation between mainland and island populations. Together these results suggest that the island populations examined are on independent evolutionary trajectories, the traits considered have a genetic basis (rather than phenotypic variation being solely due to phenotypic plasticity). Coupled with the previous results showing significant phenotypic differentiation between the island and mainland groups in this system, this study suggests that the ISH can hold even on a small spatial scale.
... To estimate predation pressure, we collated data on the average specific richness of sympatric avian predators across the range of each species [23][24][25][26][27][28][29] and computed predator-prey mass allometry relationships to exclude some predators based on size mismatch with potential preys [23,30] (electronic supplementary material, appendix S3). Predator densities or species-specific estimates of raptor-driven mortality would provide additional resolution but are not available for such a large-scale study. ...
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The character release hypothesis – which predicts that a decline in interspecific competition leads to the expansion of trait expression – remains to be tested for communication signals. Taking advantage of the fact that oceanic islands host fewer species than the mainland, we tested whether island birds show an increase in frequency bandwidth of acoustic signals compared to mainland birds. Given the higher animal diversity and more saturated acoustic space in the tropics, we expected acoustic character release, if any, to be stronger in the tropics than in the temperate zone. We field recorded 22 bird species (11 pairs consisting of an endemic island species and its closest mainland relative) breeding at similar latitudes and in similar habitats: 6 tropical pairs (São Tomé Island / Mount Cameroon), and 5 temperate pairs (Madeira Island / southern France). For each species, we measured the degree of acoustic interference experienced when vocalizing, and the spectral characteristics of its song (minimum and maximum frequencies, bandwidth). As expected, island species spent more time vocalizing alone, and any overlap in vocalizations involved fewer species. The vocalizations of island species spanned broader frequency bandwidths than their mainland counterparts in the tropics (true for all 6 pairs), but this pattern was less evident in the temperate region (2/5 pairs with no marked differences and 1/5 with opposite pattern). Overall, the character release of communication signals only occurred where the differential in number of species was large (tropics). We discuss latitude differences and the potential factors driving the observed differences.
... Therefore, they usually host a diminished sample of the continental fauna, with their smaller sizes supporting a lower richness of species (Triantis et al., 2012). However, the species that do occupy them are often extremely abundant, and display signs of rapid morphological and behavioral evolution (Pafilis et al., 2009a(Pafilis et al., , 2009bRaia et al., 2010;Li et al., 2014;Slavenko et al., 2015;Itescu et al., 2018). On the smallest islets, typically the only terrestrial vertebrates found are reptiles (Valakos et al., 2008). ...
Small islets in the Mediterranean Sea are often home to reptiles, typically representing an impoverished sample of the continental fauna, yet with high population densities and signs of rapid morphological and behavioral evolution. In this paper, we present the first herpetofaunal survey of several small islet clusters in close proximity to the Mediterranean coast of Israel, only recently geologically separated from the mainland. We performed surveys of five islets during March of 2017 – 2018 and recorded the presence of five different species of reptiles on four of the surveyed islets. Species richness varied between 1 and 4 species, and appeared to be correlated with island area, with a distinct nested structure. Reptile species may have colonized the islets by natural dispersal from nearby coastal populations, or by hitch-hiking on fishing boats and similar methods of human-assisted dispersal. Alternatively, the recorded reptiles may represent relictual populations from earlier geologic periods, when lower sea-levels supported continuous land-bridges between the islets and the mainland. These insular reptile populations require further study to establish the exact means of colonization and describe if and how they differ from mainland populations. We stress the importance of such small Mediterranean islets such as these as centers of unique biodiversity and encourage future study and conservation action aimed at them and similar islets.
... Mediodactylus kotschyi thus seems to be neither a generalist nor a specialist per se. It is probable that its great variation in a suite of morphological, ecological, and life-history traits (Valakos and Vlachopanos 1989;Valakos and Polymeni 1990;Slavenko et al. 2015;Itescu et al. 2017Itescu et al. , 2018Schwarz et al. 2020) has contributed to it becoming the most common reptile on the Aegean Islands, occupying even the smallest of islets. Our study suggests that the dichotomy of the specialist versus generalist categorization may be inadequate and oversimplified when describing the ecology and population dynamics of a species. ...
Populations of the same species occupying different microhabitats can either exhibit generalized traits across them or display intraspecific variability, adapting to each microhabitat in order to maximize performance. Intraspecific variability contributes to the generation of diversity, following selection and adaptation, and understanding such variability is important for comprehending how individuals choose their microhabitats. Compared to interspecific variability, however, intraspecific variability in functional morphology and its relationship with microhabitat preference and use have been relatively little studied. Here we examined whether populations of the gecko Mediodactylus kotschyi that differ in the substrates they occupy, display habitat-specific behaviours and differing morphologies associated with functional adaptation to their microhabitats. We collected 207 geckos from under or on rocks or on trees from seven populations in Greece. On large islands individuals occupy both substrates; whereas small islets are devoid of trees and the geckos are restricted to rocks, while on the mainland they are only found on trees.We determined gecko substrate preferences in the lab, together with their clinging abilities to the different substrates. We measured their limbs, digits and claws and assessed how these measurements relate to clinging ability.Geckos from all populations preferred the tree made available to them, but this preference was not statistically significant. Geckos from both large and small islands clung better to the tree than to the rock in the lab, while those from the mainland clung similarly to both substrates. Geckos collected from trees had longer manual digits and hind limbs. Geckos collected from large and small islands had taller (longer on the dorso-ventral axis; henceforth "deeper") claws. Longer digits and deeper but shorter claws were associated with a better ability to cling to rocks. Our findings suggest that while M. kotschyi is potentially preferentially arboreal, due to the great variation and plasticity it possesses, it can successfully also exploit the habitats available on the smallest, treeless islets in the Aegean Sea. Our study suggests that the dichotomous use of generalist vs. specialist in describing species' habitat use is oversimplified, and we suggest the use of a generalist-specialist gradient instead.
... Lister & Hall 2014), reptiles (e.g. Novosolov et al. 2012;Novosolov & Meiri 2013;Slavenko et al. 2015), and birds (e.g. Wang et al. 2009;Covas 2012;Ramos 2014). ...
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Les environnements insulaires, discontinus et généralement plus simples que les systèmes océaniques ou continentaux, ont permis le développement et la mise en place de plusieurs théories en écologie. Ainsi, les études en biogéographie sont devenues de plus en plus précises quant à l'étude des dynamiques insulaires, multipliant les facteurs explicatifs, jusqu'à tenir compte des variations interindividuelles au sein des populations. L‘hypothèse du syndrome insulaire avance ainsi l‘idée que le phénotype des individus vivants sur les îles diffère de celui des individus continentaux, et ce à cause de plusieurs caractéristiques écologiques spécifiques aux îles. Cependant, les résultats des études empiriques ayant testées les prédictions du syndrome insulaire n‘offrent pas de consensus sur la validité ou non du syndrome. Cela est très probablement dû au fait que premièrement peu d‘études prennent en compte les différents niveaux d‘organisation biologiques de manière simultanée et ensuite parce que l‘hypothèse du syndrome insulaire est basée sur un modèle verbal déductif, offrant un pouvoir prédictif limité. Le but de ce doctorat est de mesurer les changements phénotypiques des individus vivant au sein d‘un paysage fragmenté et d‘étudier les causes de ces éventuels changements. Cela à partir de mesures phénotypiques effectuées sur deux espèces de petits mammifères : la souris sylvestre (Peromyscus maniculatus) et le campagnol à dos roux de Gapper (Myodes gapperi), ainsi que des relevés des caractéristiques du paysage, des communautés et des populations au sein d‘un milieu naturellement fragmenté. Chez les souris, nous avons montré que le phénotype des individus était largement affecté par la vie sur les îles, en comparaison des individus continentaux. Ainsi les individus vivant sur les îles étaient moins agressifs envers de potentiels prédateurs, ils étaient des explorateurs plus minutieux, les mâles étaient plus lourds et les juvéniles avaient des queues plus longues. En revanche les campagnols ne semblaient quasiment pas affectés par la vie insulaire. Nous avons également mis en évidence l‘impact de la surface, de l‘isolement et de la connectivité des parcelles sur ces traits phénotypiques chez la souris sylvestre. Dans un second temps nous avons mis en évidence chez la souris sylvestre que les individus disperseurs avaient un phénotype différent des individus résidents lorsqu‘il s‘agissait de jeunes adultes. Nous avons également montré que les parcelles d‘émigrations et d‘immigrations avaient des caractéristiques particulières. Enfin nous avons mis en évidence, pour les souris, que les caractéristiques du paysage (c.-à-d. surface et isolement des parcelles) avaient des impacts sur certaines dimensions des communautés, qui affectaient à leur tour les caractéristiques des populations. En revanche, les populations de campagnols étaient très peu affectées. Finalement nous avons démontré que ces changements liés à l‘insularité des parcelles étaient en partie responsables des modifications phénotypiques précédemment trouvées chez les souris sylvestre. Ce doctorat a permis de mettre en évidence la complexité des liens entre les différents niveaux d‘organisation biologique : du paysage jusqu‘au phénotype des individus. Il a également permis de valider certaines prédictions du syndrome insulaire mais d‘autres prédictions ont été infirmées dans notre aire d‘étude. Ce travail de doctorat a ainsi pu appréhender les causes écologiques responsables du maintien de la variabilité comportementale interindividuelle au sein d‘un paysage naturellement fragmenté.
... 1,2,5). Some examples are the studies that deal with the direct or indirect influence on invertebrates (Polis and Hurd, 1995;Sánchez-Piñero and Polis, 2000;Markwell and Daugherty, 2002;Harding et al., 2004;Gardner-Gee and Beggs, 2009;Hawke and Clark, 2010;Bassett et al., 2014) or vertebrates (reptiles: Markwell and Daugherty, 2002;Barrett et al., 2005;Spiller et al., 2010;Slavenko et al., 2015;rabbits: Gillham, 1963;wood mouse: Bicknell et al., 2020;other birds: Vidal et al., 1998c). These effects are more pronounced in small areas such as small islands Hurd, 1995, 1996;Polis et al., 1997;Sánchez-Piñero and Polis, 2000;Polis, 2003a, 2003b;Harrison, 2006). ...
... To estimate predation pressure, we collated data on the average specific richness of sympatric avian predators across the range of each species [23][24][25][26][27][28][29] and computed predator-prey mass allometry relationships to exclude some predators based on size mismatch with potential preys [23,30] (electronic supplementary material, appendix S3). Predator densities or species-specific estimates of raptor-driven mortality would provide additional resolution but are not available for such a large-scale study. ...
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Insular ecosystems share analogous ecological conditions, leading to patterns of convergent evolution that are collectively termed as the ‘island syndrome’. In birds, part of this syndrome is a tendency for a duller plumage, possibly as a result of relaxed sexual selection. Despite this global pattern, some insular species display a more colourful plumage than their mainland relatives, but why this occurs has remained unexplained. Here, we examine the hypothesis that these cases of increased plumage coloration on islands could arise through a relaxation of predation pressure. We used comparative analyses to investigate whether average insular richness of raptors of suitable mass influences the plumage colourfulness and brightness across 110 pairs of insular endemic species and their closest mainland relatives. As predicted, we find a likely negative relationship between insular coloration and insular predation while controlling for mainland predation and coloration, suggesting that species were more likely to become more colourful as the number of insular predators decreased. By contrast, plumage brightness was not influenced by predation pressure. Relaxation from predation, together with drift, might thus be a key mechanism of species phenotypic responses to insularity.
I assessed the effect of island characteristics and population isolation on the endemic insular lizard Podarcis erhardii and its native hemogregarine parasite Hepatozoon spp. I analyzed the relationships of prevalence, infection likelihood, and parasitemia to several factors at the island (time of isolation, area, distance to nearest larger land mass), population (host density), and organismal (load of hematophagous ectoparasites) levels. My results suggest that smaller islands, as well as islands that have been isolated for longer periods of time, show higher infection rates and higher parasitemia in hosts than others. I also found that distance between a focal island to the nearest larger land mass, as well as the load of hematophagous ectoparasites on an individual, were poor predictors of infection variables in P. erhardii. These results indicate that island area, host population density, and island age are likely to be significant drivers of changes in host-parasite interactions in fragmented populations.
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Many life‐history traits co‐vary across species, even when body size differences are controlled for. This phenomenon has led to the concept of a “fast‐slow continuum,” which has been influential in both empirical and theoretical studies of life‐history evolution. We present a comparative analysis of mammalian life histories showing that, for mammals at least, there is not a single fast‐slow continuum. Rather, both across and within mammalian clades, the speed of life varies along at least two largely independent axes when body size effects are removed. One axis reflects how species balance offspring size against offspring number, while the other describes the timing of reproductive bouts.
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Sixteen populations of Cyrtopodion kotschyi from the Italian range of the species (central and southern Apulia and eastern Basilicata) were sampled to infer conservation guidelines. The species is still common, particularly in Lower Murgia where large populations are found along stone walls bordering farms, except for the suburbs of Bari, where it is probably extinct. The main causes of species' decline are urbanisation, modern agriculture, trasformation of landscape and use of biocide that menace most populations. A status of “vulnerable” is suggested for the Italian stock. A conservation plan should include habitat protection, abundance and genetic monitoring, and the creation of corridors to allow genetic exchange. The protection and restoration of the rural stone walls network would help to reach these purposes.
Islands with large colonies of seabirds are found throughout the globe. Seabird islands provide nesting and roosting sites for birds that forage at sea, deposit marine nutrients on land, and physically alter these islands. Habitats for numerous endemic and endangered animal and plant species, seabird islands are therefore biodiversity hotspots with high priority for conservation. Successful campaigns to eradicate predators from seabird islands have been conducted worldwide. However, removal of predators will not necessarily lead to natural recovery of seabirds or other native species. Restoration of island ecosystems requires social acceptance of eradications, knowledge of how island food webs function, and a long-term commitment to measuring and assisting the recovery process. This book provides a large-scale cross-system compilation, comparison, and synthesis of the ecology of seabird island systems.