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The reproductive strategy of Podarcis milensis exhibits some peculiarities when compared with other congeners. Males and females attain sexual maturity at a minimum body size of 47 and 42 mm SVL, respectively, both at an age of about one year. Podarcis milensis has a very small clutch size, with a mean of 1.73 and a range of 1–3 eggs, and produces multiple clutches annually. Both sexes exhibit a prolonged reproductive period extending from January to August.
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2000 by the American Society of Ichthyologists and Herpetologists
Copeia, 2000(2), pp. 610–614
Small Clutch Size in a Mediterranean Endemic Lacertid
(Podarcis milensis)
C. A
E. D. V
The reproductive strategy of Podarcis milensis exhibits some peculiarities when
compared with other congeners. Males and females attain sexual maturity at a min-
imum body size of 47 and 42 mm SVL, respectively, both at an age of about one
year. Podarcis milensis has a very small clutch size, with a mean of 1.73 and a range
of 1–3 eggs, and produces multiple clutches annually. Both sexes exhibit a pro-
longed reproductive period extending from January to August.
EMBERS of the family Lacertidae are
widespread in the Old World, being dis-
tributed over Europe, Africa, and parts of Asia.
The family comprises over 230 specieswhich are
assigned to about 30 genera (Arnold, 1989). Re-
productive traits of European lacertids, espe-
cially from the western Mediterranean region,
have been well documented by various authors
(Pollo and Pe´rez-Mellado, 1990; Castilla et al.,
1991; Carretero and Llorente, 1997), whereas
life-history information on lizards occurring in
the eastern Mediterranean are poorly known
and for only a few species (Chondropoulos and
Lykakis, 1983; Valakos, 1990).
In this paper, we describe the unusual repro-
ductive cycle of Podarcis milensis, a lizard endem-
ic to the Aegean Archipelago (Greece). This
knowledge is valuable for its conservation and
protection, since the species is the only small
lacertid in the area.
Species.—Podarcis milensis is restricted to the Mi-
los Island group (Milos, Kimolos, Polyaigos, An-
timilos, and islets). It is a small but robust lizard
with a characteristic blue color pattern in males.
The species remains active all year. It is mostly
a ground dweller, exhibiting dense populations
both in open sandy areas such as sand dunes
and in cultivated land.
Study area and climate.—The study area is located
in the center of Milos Island (24
in a sandy coastal area between the sea and
Lake Achivadolimni. Vegetation consists almost
entirely of Thymus sp. and Juniperus oxycedrus
ssp. macrocarpa. Podarcis milensis is extremely
abundant and uses the small bushes of the area
for shelter. The climate is considered semiarid
Mediterranean, with annual rainfall varying
from 0 to 200 mm. A dry season exists from May
through October. The annual temperature, ac-
cording to the meteorological station on the is-
land, ranges from 10 C to 26 C (min
31.5 ). However, in the study area, the air
temperature in summer reaches 37–38 Cat mid-
Field and laboratory methods.—A total of 341 adult
lizards (218 females and 123 males) were in-
cluded in the study, all coming from Milos Is-
land. Of these, 182 animals came from museum
collections, whereas the remaining 159 came
from the study site. After capture, specimens
were weighed to the nearest 0.1 g with a Pesola
balance and processed immediately. In the lab-
oratory, the following measurements were taken
for each specimen: SVL (to 1 mm), longest and
shortest axes of the right testis, number and di-
ameter of ovarian follicles and number, length
and width of oviductal eggs. Female sexual ma-
turity was assessed by the presence of enlarged
vitellogenic follicles (more than 3 mm in di-
ameter) or oviductal eggs, whereas the simul-
taneous presence of large vitellogenic follicles
and oviductal eggs was considered evidence for
multiple clutches. The size at sexual maturity
for males was estimated by the presence of sec-
ondary sexual characters such as the character-
istic light blue color of the throat. All field spec-
imens were deposited at the Zoological Muse-
um of the University of Athens. The same mea-
surements were taken for museum specimens
previously collected (see Materials Examined).
The mean length of the nine eggs deposited in
the laboratory was 15.3 mm (range
1.11) and the mean width 8.0 mm
7–9, S.D.
0.64). Only eggs matching
or exceeding these parameters were used in es-
timating egg size and volume from preserved
animals. Estimates of testis and egg volumewere
obtained using the formula for the volume of
an ellipsoid.
Age classes for females were determined by
the von Bertalanffy equation and were as follows
(Adamopoulou, 1999): (1)
44 mm SVL; (2)
53 mm; (3) 53
57 mm;
Fig. 1. Annual variation of testis volume:SVL ratio
in adult males of Podarcis milensis. Sample size is in-
dicated above each month.
1. P
Podarcis milensis F
1, 2,
. Mean SVL, mean clutch size, and mean egg length for each class (with range and SD) are
shown in the first three columns. The sample size for each class is given in parentheses.
Age class Mean SVL (mm) Mean clutch size Mean egg length (mm)
Clutch size
(%) 3
I (17) 42.6, (42–3.5), SD
0.55 1.66, (1–2), SD
0.57 15, SD
0 33.3 66.7
II (129) 48.6, (44–52), SD
2.47 1.72, (1–3), SD
0.58 16.2, (14–20), SD
1.49 34.7 58.7 6.6
III (54) 54.5, (53–56.5), SD
1.06 1.77, (1–3), SD
0.74 15.4, (14–18), SD
1.12 41 41 18
IV (18) 58.0, (57–61), SD
1.07 1.66, (1–3), SD
0.7 18.0, (17–21), SD
1.77 44.4 44.4 11.2
and (4)
57 mm. We determined the time of
hatching and SVL of hatchlings in the field by
the presence of a ventral navel scar (Gala´n,
Comparisons between the two samples (mu-
seum and field specimens) were made using
analysis of covariance (ANCOVA) with SVL as
the covariate. The relationships between clutch
size, female body size, and mean egg volume
were examined using linear regression analyses,
whereas monthly changes in testis/SVL ratio
were assessed using analysis of variance (ANO-
In general, P. milensis males are larger than
females. In our sample, the mean SVL for adult
males was 56.7 mm (range
47–68, SD
123), and the mean SVL for adult females
was 50.4 mm (range
42–61, SD
4.42, n
Testing the two samples.—We found no significant
differences between museum and field speci-
mens in clutch size (F
2.20, P
egg length (F
0.81, P
0.05), egg width
0.24, P
0.05), mean egg volume
1.15, P
0.05), number of large vitel-
logenic follicles (F
0.02, P
0.05), or tes-
tis volume (F
0.5, P
0.05). Therefore,
the two samples were pooled together for fur-
ther analysis.
Males.—Minimum size at sexual maturity was
found to be 47 mm SVL. Testes exhibit their
maximum volume in January and February. Af-
ter a period of stability at slightly smaller sizes
from March to May, testes volume decreased in
June and reached minimum size in July, with
recrudescence beginning in August. A second
gradual decrease in testes volume began in No-
vember and continued through December, fol-
lowed by a rapid increase to maximum values
in January (Fig. 1). There was a significant dif-
ference between months in testes volume/SVL
ratio (ANOVA, F
3.63, P
Females.—The smallest reproductive female
measured 42 mm SVL which, according to our
estimations, was reached by most females at the
age of 12 months. The mean clutch size (based
on oviductal eggs) was 1.73 (range
1–3, SD
0.64, CV
0.36, n
126). The mean second
clutch size was 1.27 (range
1–3, SD
0.53, n
29) and was significantly different from the
first one (t-test, t
3.56, P
0.05). The average
egg length was 16.1 mm (range
14–21, SD
1.521, CV
0.09, n
62) and the average egg
width 8.2 mm (range
7–11, SD
0.738, CV
0.09, n
82). According to our field obser-
vations, the first hatchlings appear at the end of
April and the last at the end of September. They
have an SVL of 24–31 mm.
Females of all age classes did not differ in
clutch size (F
0.927, P
0.05), number
of enlarged vitellogenic follicles (F
0.05), or width of oviductal eggs (F
1.065, P
0.05). There was a significant differ-
ence between age classes in egg length (F
3.795, P
0.05); larger females of class 4 car-
ried the longest eggs of all female age classes
(Table 1).
In Figure 2, the percentage of sexually ma-
612 COPEIA, 2000, NO. 2
Fig. 2. Seasonal variation in the percentage of sex-
ually mature females in Podarcis milensis (n
Females with (A) oviductal eggs, (B) oviductal and
large vitellogenic follicles (
3 mm), (C) large vitel-
logenic follicles (
3 mm), (D) without reproductive
2. R
Podarcis milensis. Reproductive season was
estimated by the first and last appearance of oviductal eggs whereas evidence for later clutches was given by
the simultaneous presence of oviductal eggs and large vitellogenic follicles. The sample size is given in paren-
Female classes
Reproductive season
according to the presence of
oviductal eggs Evidence for later clutches
I (17) May
II (129) April–July April, May, June, July
III (54) January–July April, May, June
IV (18) January–August February, March, May, June, August
ture females with or without reproductive activ-
ity is plotted for each month from January on-
ward with a peak in May and a gradual decline
toward August. In May, almost 90% of the fe-
males in our sample were reproducing.
The smallest females start their reproductive
activities in May (Table 2). It seems that they
have no second clutch, although this may be
due to the small sample examined. Females of
the second class, which represents the majority
of the population, have large vitellogenic folli-
cles from March onward, whereas we have evi-
dence for further clutches in April to July. The
larger females of the third and fourth age class
start their reproductive activity in January and
end in August. Females of the fourth age class
carry eggs from February to August. Beginning
in October, all females were reproductively in-
active. The simultaneous occurrence of oviduc-
tal eggs and enlarged vitellogenic follicles dur-
ing most months of the reproductive season
confirms that at least a proportion of individual
females produce at least two clutches per year.
There was no significant correlation between
clutch size and female SVL (r
0.09, R
0.008, P
0.05) or female SVL and mean egg
volume (r
0.152, R
0.023, P
0.05), but
mean egg volume was significantly inversely cor-
related with clutch size (r
0.475, R
Podarcis milensis, compared to other Podarcis
species, exhibits an exceptionally small clutch
size in combination with the capability of pro-
ducing more than one annual clutch. Bauwens
and ´az-Uriarte (1997) analyzed patterns of
lacertid life-history variation and proposed that
species within this clade can be arranged along
a single, multivariate axis. Podarcis milensis clear-
ly is placed at one end of this continuum as a
small-sized species that matures early and has
small clutches of relatively large young, multiple
broods per year, and a short adult lifespan.
The species displays a prolonged reproduc-
tive period extending from January to the end
of summer. During both years of this study,
large females were seen either pregnant or cop-
ulating in January. Males P. milensis exhibit a re-
productive cycle synchronized with that of fe-
males. Podarcis milensis is the first European lac-
ertid to our knowledge having such an extensive
breeding season and small clutch size. Other
Mediterranean Podarcis species studied (P. erhar-
dii, Naxos Island, Valakos, 1990; P. taurica, Io-
nian archipelago, Chondropoulos and Lykakis,
1983; P. bocagei, Iberian peninsula, Gala´n, 1996;
P. pityusensis, northeast Spain, Carretero et al.,
1995; P. atrata, Columbretes islands, Bauwens
and ´az-Uriarte, 1997) have shorter breeding
seasons, larger clutch sizes, and larger SVLs at
reproductive maturity.
The fact that no significant relationship be-
tween SVL and either clutch size or mean egg
volume was found implies that P. milensis has
reached an evolutionarily optimum egg volume
and clutch size, showing no increase in the two
variables with an increase in body size. The neg-
ative correlation between mean egg volume and
clutch size may reflect the extent to which fe-
male P. milensis ‘burden’’ themselves with eggs.
For example, the space available for eggs in the
body cavity of females may place an upper limit
on their volume (Shine, 1992). To avoid pro-
ducing nonviable eggs or hatchlings, females
must increase egg size at the expense of clutch
It seems that for some reason P. milensis has
evolved a low and quite invariable clutch size,
producing large eggs in relation to those of oth-
er lacertids for which data are available. Never-
theless, small clutch size may not be an adap-
tation but the consequence of selection on oth-
er life-history parameters such as large offspring
size. Larger eggs produce larger young which in
turn have a survival advantage over smaller ones
(Ferguson and Fox, 1984; Sinervo, 1990). If this
is the case in P. milensis, high intraspecific com-
petition might increase selection for large eggs
with the potential for enhanced offspring sur-
vival rather than larger clutch size. Population
density at the study site reaches a level of 550–
600 animals/ha (Adamopoulou, 1999), which is
considered high, the consequences of which are
manifested in at least two ways.First, adultmales
have been seen expressing aggressive behavior
toward juvenile males both in the laboratory
and in the field, even killing them instantly by
neck biting when put together. Second, canni-
balism (whole hatchlings in the stomach) has
been detected in adult males. Alternatively, the
effect of high predation on adult lizards might
result in selection for early reproduction (Gadg-
il and Bossert, 1970), which is associated with
small clutch size and more than one clutch per
season (Tinkle et al., 1970). Indeed, adult P. mil-
ensis are exposed to a similar array of predators
as are continental species (Pe´rez-Mellado et al.,
1997), including birds of prey and three species
of snakes such as the Blunt-Nosed Viper Macro-
vipera schweizeri, 21.4 % of the diet of which con-
sists of P. milensis (Adamopoulou et al., 1997).
On the other hand, low clutch number is as-
sociated in this species with the potential for
frequent ovipositions, which is favored by weath-
er conditions that probably favor the extension
of the reproductive season. In winter, individual
P. milensis take advantage of numerous sunny
days to bask, since the air temperature in the
sand dune of Achivadolimni reaches 20 C in
January and February.
To summarize, we cannot offer a single ex-
planation for the evolution of low clutch size in
P. milensis. However, considering the ability of
the species to produce multiple clutches, the
most plausible mechanism for producing more
offspring may be to increase clutch frequency,
thus spacing clutches temporally and spatially.
Selection may have favored the evolution of op-
portunistic reproductive behavior in females, in
which energy is invested not in the number or
size of eggs per clutch but in their frequency,
thus taking complete advantage of favorable cli-
matic conditions within the constraints of age
and physiological state. The extended isolation
of the Milos Islands group (since the upper
Pleistocene; Papanikolaou and Dermitzakis,
1981) may have enabled P. milensis to develop a
more efficient reproductive strategy than the
other Podarcis species of the Aegean with regard
to the special climatic conditions of insular
Mediterranean-type ecosystems.
Institutional abbreviations are as listed in Lev-
iton et al. (1985). The specimen number is fol-
lowed by the collecting locality and the month
and year of collection as noted on the labels:
ZMFK 1657–1711, ZMFK 1742–1801 (Milos, 5/
1953), ZMFK 30999–31030 (Milos, 6/1956),
NMW 15257:1–15257:29 (Milos, 5/1954), NMW
24035:6–24035:14 (Milos, 7/1979), NMW 11
452:1–11452:11 (Milos, 7/1932).
We thank W. Bo¨hme [Herpetological Collec-
tion of the Alexander Koenig Zoological Insti-
tute and Museum (Bonn, Germany)] and F. Tie-
demann and H. Grillitsch (Naturhistorisches
Museum of Wien) who kindly allowed us to ex-
amine Podarcis milensis specimens. We also thank
two anonymous reviewers for their useful com-
ments. This study was supported by the General
Secretariat for Research and Technology, proj-
ect 1298/95ED. The collection of specimens
was carried out according to Presidential De-
cree 67/81.
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reprint requests to CA. Submitted: 23 Sept.
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A. H. Price.
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... The so-called island syndrome predicts a shift to the production of fewer, but larger offspring (Adler & Levins, 1994;Blondel, 2000). Podarcis milensis follows this pattern and produces only 1-3 eggs (Adamopoulou & Valakos, 2000) and similar small clutch sizes have been reported for P. erhardii (Valakos, 1991). Insular lizards compensate for the smaller egg number with more frequent clutches (Schwarz & Meiri, 2017). ...
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Aegean Islands host a rich herpetofauna comprising a plethora of endemic taxa. Since the early 19th century, this unique diversity attracted numerous herpetologists that described the Greek species and provided records of their distribution. Interestingly, many new records on insular ranges are still added to the literature every year. During the last two decades, modern Systematics use powerful tools from the arsenal of molecular biology to unravel complicated phylogenies and shed light to hidden diversities. Current herpetological research focuses on the detection of cryptic species, yielding impressive findings. Another important research avenue includes the clarification of the particular adaptations that insular species adopted to survive under the demanding conditions of the Aegean Islands. Food scarcity, water dearth, high temperatures, relaxed predation and strong intraspecific competition are the main parameters shaping the ecophysiological profile of Aegean herptiles. However, the amphibians and reptiles of the Archipelago have to deal with serious threats. The most severe among them are habitat degradation and the loss of breeding-sites due to human activities and climate change. New phylogenetic data and well-justified gene trees together with the ongoing enhancement of our knowledge of species biology pave the way for the effective conservation of the matchless Aegean herpetofauna.
... Snake-eyed Skink reaches sexual maturity approximately at the age of two, and lives up to 3.5 years (Gruber 1981). This is opposing the theory that short-lived animals reach sexual maturity sooner and commonly have more than one clutch per year in order to maximize the number of offspring during their life span (Adamopoulou & Valakos 2000). We European lacertid species (Bosch & Bout 1998), and it was also confirmed in our case. ...
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The most western population of the Snake-eyed Skink, discovered recently on Papuk Mountain and Ilok area in Croatia, has never been studied before. Here we examined the morphology and age structure, reproduction, and prevalence of injuries in both populations. We examined 191 individuals in total; 163 adults and 28 juveniles. Morphological analysis was based on 140 adult individuals (129 from Papuk, 11 from Ilok) and 34 juveniles (21 caught in the wild and 13 hatched in captivity). Our results showed that although there is no clear sexual dimorphism, adult animals exhibit slight difference between sexes. In adult individuals in Papuk 34.1 % and in 35 % in juveniles, a tail has been regenerated, while in Ilok in 27.3%. From 2010-2012 nine gravid females collected from Papuk Mountain deposited eggs in the lab. Number of eggs in each clutch was recorded, and each egg was weighed and measured, and the measurements were taken regularly until hatching. Clutch size spanned between 2-4 eggs with an average of 2.78 eggs. Of 25 deposited eggs, 9 eggs did not develop. Monitoring of egg sizes showed that average length, width, mass, surface and volume increase linearly during the incubation time, but the growth was allometric. The bigger the size of a female does not result in increased number of eggs, but in increased individual egg size.
... Though most Podarcis species have both mainland an insular populations, 10 of them are strictly endemic to Mediterranean islands. The overall biology of these species depart in many aspects from their mainland peers, including thermal biology (Grbac and Bauwens, 2001;Adamopoulou and Valakos, 2005), feeding ecology (Salvador, 1986;Capula and Luiselli, 1994), life history (Adamopoulou and Valakos, 2000;Castilla and Bauwens, 2000), digestive performance (Pafilis et al., 2007, in press), defensive tactics (Pafilis et al., 2009a;Li et al., 2014), and behavior (Pérez-Mellado et al., 2000;Traveset and Riera, 2005;Cooper et al., 2009;Brock et al., 2014a). Podarcis islanders differ in the limits of their range. ...
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The ecological importance of islet endemics are in the front line of conservation efforts and thus the good knowledge of their biology is required. Podarcis levendis is a lacertid lizard, endemic to two rocky islets in the Cretan Sea, Greece, that was raised to specific level in 2008 and since then no data on its biology are available. Here we present the first ecological information on the species, focusing on population density, tail autotomy and feeding preferences. We recorded regenerated and damaged tails in the field and estimated population density with the transect method. We also dissected museum specimens and analyzed their stomach content. Regenerated tails were common and reached a considerable 71%. The latter finding could be attributed to the intense intraspecific competition due to high population density but also to the seasonal predation pressure by migratory birds. The diet of P. levendis coincides with that of other insular congenerics, including high percentages of plant material.
... The so-called island syndrome predicts a shift to the production of fewer, but larger offspring (Adler & Levins, 1994;Blondel, 2000). Podarcis milensis follows this pattern and produces only 1-3 eggs (Adamopoulou & Valakos, 2000) and similar small clutch sizes have been reported for P. erhardii (Valakos, 1991). Insular lizards compensate for the smaller egg number with more frequent clutches (Schwarz & Meiri, 2017). ...
... Consequently, males reached sexual maturity at a similar age and matured at a larger size than females. Although this pattern is observed in many other Podarcis species (Bocage's Wall Lizard, Podarcis bocagei (Seoane, 1884): Galán 1999; Milos Wall Lizard, Podarcis milensis (Bedriaga, 1882): Adamopoulou and Valakos 2000;Carbonell's Wall Lizard, Podarcis carbonelli Pérez-Mellado, 1981: Almeida et al. 2001Common Wall Lizard, Podarcis muralis (Laurenti, 1768): Bauwens and Díaz-Uriarte 1997), the common pattern observed in many reptiles is a positive correlation in sex differences between sexual size maturity and asymptotic maximum size (Trivers 1976;Schoener and Schoener 1978;Gibbons and Lovich 1990;Stamps 1993). A common K value for males and females indicates that environmental factors affecting the growth of males have similar effects on females (Stamps 1993). ...
The body growth rate in small reptiles is modulated by per-capita food resources and recent evidences suggested that this constraint is the mechanism underlying differences between cohorts. Per-capita food resources depend on population size and climatic factors but their relative role in explaining the variations in growth rate is unclear. We used morphological data collected over six years to model the body growth of an insular lizard (Podarcis lilfordi Günter, 1874). We used non-linear equations to describe the appropriate length-at-age relationship. For each sex, seasonal growth was observed and the oscillatory Von Bertalanffy curve was fitted to the data. Three age classes were recognized, and we investigated the relative role of density, spring rainfall and temperature in explaining the variation of the growth rate in each sex-by-age class. Results showed that the relative role of density and climatic factors varied according to the age considered. While population size and temperature had a negative effect in the growth rate of juveniles, rainfall had a positive influence for the growth of sub-adults. Adult growth was near zero and constant over time. The different role of density-dependent and climatic factors in explaining age-dependent growth rate provides an important insight in understanding lizard population dynamics and life-history tactics.
Insular animals are thought to be under weak predation pressure and increased intraspecific competition compared with those on the mainland. Thus, insular populations are predicted to evolve 'slow' life histories characterized by fewer and smaller clutches of larger eggs, a pattern called the 'island syndrome'. To test this pattern, we collected data on egg volume, clutch size and laying frequency of 31 Aegean Island populations of the closely related geckos of the Mediodactylus kotschyi species complex. We tested how predation pressure, resource abundance, island area and isolation influenced reproductive traits. Isolation and predation were the main drivers of variation in life-history traits. Higher predator richness seemed to promote faster life histories, perhaps owing to predation on adults, whereas the presence of boas promoted slower life histories, perhaps owing to release from predation by rats on the eggs of geckos. Insular geckos followed only some of the predictions of the 'island syndrome'. Predation pressure seemed to be more complex than expected and drove life histories of species in two opposing directions. Our results highlight the importance of considering the identity of specific predators in ecological studies. ADDITIONAL KEYWORDS: Aegean Islands-clutch frequency-clutch size-egg volume-geckos-island biology-island syndrome-life-history traits.
The Miocene sediments of Zakynthos, Epirus, western Thessaly, Crete and Cyclades are described as well as their geotectonic position within an evolving island arc system. A comparison between two segments of the arc is made for the Burdigalian and the Messinian times. A very similar geometry is observed in both segments during Burdigalian, which is destroyed during Messinian. The geometry of the southern segment of the arc during Burdigalian and Messinian was similar to the actual geometry whereas the same geometry existed in the northern segment only during Burdigalian. This differentiation of the southern segment of the Hellenic Arc was initiated during Langhian-Tortonian and it is related with the final collision between Arabia and Europe and with the consequent movement of the surrounding areas towards the WSW. -Author
Podarcis taurica ionica is the dominant lizard species on most Ionian islands and is abundant in the western Greek mainland. Population densities range between 82 and 365 lizards/ha. The species occupies primarily habitats with low vegetation and is characterized by a high degree of seasonal color adaptation to its environment as well as by poor climbing ability in comparison with other Wall Lizards of the Balkans. Daily activity is bimodal during the largest part of the annual activity period. Many individuals (27.78-57.14%) show broken tails but both interpopulation and intersexual differences of injury frequencies are not significant. Hibernation usually lasts from early Nov. to late Feb. or early March. Most copulations are observed from early April to early May. Females with oviductal and/or large ovarian eggs are present mainly from mid April to mid July, but the peak of gestation occurs from mid May to mid June. Normally there are two clutches per season. The first oviposition occurs from mid May to early June and the second one from mid June to mid July. Hatching usually takes place from mid July or early Aug. to early Sept., after an incubation period of about 8-9 weeks. Sex ratio is usually near 1:1, and observed deviations are not significant. Reproductive maturity in females is attained at an approximate snout-vent length (SVL) of 52-56 mm, which corresponds to an age of 18-20 months. Clutch size ranges from 2 to 10 eggs (usually from 3 to 5 eggs), and is significantly larger in mainland populations. There is a positive correlation between SVL and clutch size in most populations studied. Oviductal egg size and mass differ significantly among the populations examined but are not correlated to SVL. The ratio of egg to body mass differs significantly among some of the studied populations, but there are no differences of relative clutch mass (RCM).
Analysis of five generations of Uta stansburiana showed that larger hatchlings enjoyed increased survivorship over two weeks and to breeding age than smaller hatchlings. This advantage of large size was most apparent for survival to maturity and for lizards hatched dur- ing July 1-15, when most hatchlings appeared in the field. This period was also the time when food was often the most limiting. The degree of advantage varied among years. Results from experimental treatments on juveniles over two other years indicated that large juvenile ad- vantage was observed only during conditions of food competition and predation. Removal of predators or supplementary feeding nullified the otherwise beneficial effect of large body size during the year when control populations with natural levels of food and predation showed significant differences in body size between survivors and nonsurvivors. These results support the hypothesis that levels of either predation or resource abundance define the degree of survival advantage of larger juveniles. Even small differences in size among very young juveniles is likely to affect their interactions with conspecifics during the. acquisition of optimal home ranges. Quality of home ranges ultimately affects the probability of survival during strong selective con- ditions. If larger juvenile size is governed to some extent genetically, then selection for larger size could effect changes in time of hatching, growth of hatchlings, and size of hatchlings.
The attainment of sexual maturity by males and females of the lacertid lizard Podarcis bocagei was studied in a population from NW Spain (La Corufia province). Two methods were used. The first method involved capture, marking and recapture of marked hatchlings in a study plot. The second method examined the development of sexual organs through dissection of lizard samples from the same locality. Sexual maturity was attained at a minimum size (females: 44-45 mm; males: 46-51 mm snout-vent length), not a minimum age. Some individual and seasonal variation was observed in this minimum size, which decreased as the reproductive season progressed. Slightly fewer than half of the individuals from a given cohort (50.0%-44.4% in males and 47.1%-44.4% in females, from samples of 1989 and 1990 cohorts respectively) attained the minimum size and reproduced towards the end of the next reproductive period (at 11-12 months of age). The mature yearling individuals were those that hatched from the first clutches of the preceding year, most of them in July. By their second autumn, all specimens from the previous year's cohort had exceeded the sexual maturity-threshold size.