ABSTRACT
We used Takydromus septentrionalis, a sexually size-monomorphic lacertid lizard, as a model system to test the hypothesis that sexual size monomorphism may evolve in lizards where reproductive performance is maximized at a similar body size for both sexes. We allowed lizards housed in laboratory enclosures to lay as many clutches (for females) as they could or to mate as many times (for males) as they could in a breeding season. Size-assortative mating was weak but evident in T. septentrionalis, as revealed by the fact that male and female snout-vent lengths (SVLs) in mating pairs were significantly and positively correlated. Mating frequency (indicative of male reproductive performance) varied from 1 to 8 per breeding season, generally increasing as SVL increased in adult males smaller than 67.4 mm SVL. Clutch frequency varied from 1 to 7 per breeding season, with female reproductive performance (determined by clutch frequency, annual fecundity, and annual reproductive output) maximized in females with a SVL of 68.0 mm. Accordingly to our hypothesis, the reproductive performance was maximized in the intermediate sized rather than the largest individuals in both sexes, and the body size maximizing reproductive performance was similar for both sexes. Future work could usefully investigate other lineages of lizards with sexually monomorphic species in a phylogenetic context to corroborate the hypothesis of this study.
ABSTRACT
The reproductive maturation hypothesis, the terminal investment hypothesis, and the senescence hypothesis are the most extensively evaluated hypotheses proposed to explain age-related patterns of reproduction in iteroparous organisms. Here, we evaluated these hypotheses for the Mongolian racerunner (Eremias argus), a short-lived lacertid lizard, by comparing reproductive traits between females that completed reproductive cycles under the same laboratory conditions in two consecutive years (2008 and 2009). Reproductive females gained linear size (snout-vent length) not only as they got 1 year older but also during the breeding season. Larger females generally laid eggs earlier and invested more in reproduction than did smaller ones. Females switched from laying smaller eggs in the first clutch to larger eggs in the subsequent clutches but kept clutch size and postpartum body mass constant between successive clutches in a breeding season and between years. Females that laid more clutches or eggs in 2008 did not lay fewer clutches or eggs in 2009. Of the traits examined, only clutch frequency, annual fecundity, and annual reproductive output were susceptible to ageing. Specifically, the clutch frequency was reduced by 1.1 clutches, annual fecundity by 3.1 eggs and annual reproductive output by 1.0 g in 2009 compared with 2008. Our results suggest that the reproductive maturation hypothesis better explains patterns of reproduction in young or prime-aged females of E. argus, whereas the senescence hypothesis better explains reproductive patterns in old females. The terminal investment hypothesis does not apply to any trait examined because no trait value was maximized in old females.
Subject(s)
Aging/physiology , Fertility/physiology , Lizards/physiology , Animals , Body Size , Clutch Size/physiology , FemaleABSTRACT
Estimating the absolute number of individuals in populations and their fecundity is central to understanding the ecosystem role of species and their population dynamics as well as allowing informed conservation management for endangered species. Estimates of abundance and fecundity are often difficult to obtain for rare or cryptic species. Yet, in addition, here we show for a charismatic group, sea turtles, that are neither cryptic nor rare and whose nesting is easy to observe, that the traditional approach of direct observations of nesting has likely led to a gross overestimation of the number of individuals in populations and underestimation of their fecundity. We use high-resolution GPS satellite tags to track female green turtles throughout their nesting season in the Chagos Archipelago (Indian Ocean) and assess when and where they nested. For individual turtles, nest locations were often spread over several tens of kilometres of coastline. Assessed by satellite observations, a mean of 6.0 clutches (range 2-9, s.d. = 2.2) was laid by individuals, about twice as many as previously assumed, a finding also reported in other species and ocean basins. Taken together, these findings suggest that the actual number of nesting turtles may be almost 50% less than previously assumed.
Subject(s)
Conservation of Natural Resources , Turtles , Animals , Ecosystem , Endangered Species , Female , Geographic Information Systems , Indian Ocean , Nesting BehaviorABSTRACT
Reproductive activity of Chelonia mydas (Testudines: Cheloniidae) in Isla de Aves, Venezuela (2001-2008). The second major nesting-site for green turtles in the Caribbean is Isla de Aves, an island protected as a wildlife refuge since 1972, located at 650km Northeast from La Guaira, Venezuela. In this island, the nesting population monitoring started in 1972 and in a more continuous way after 1978, when a Scientific-Naval Station was established and scientific observations started. Since historical data show that female captures had severely affected population levels in this island before 1978, this study aim to describe recent reproductive activities. For this, during the nesting seasons of 2001-2002 and 2005-2008, nesting females were measured and tagged using metal flipper tags. A total of 458 nights were sampled observing 5 154 female emergences, with a maximum of 53 in a single night. Non-observed emergences were calculated fitting the temporal distribution of observed emergences to a normal curve. Total emergences estimated varied from =637.1±106.6 in 2001 to =2 853±42.5 in 2008 (ANOVA F(6.5df)=60.37, p<0.0001). Internesting interval in the same season was estimated in =10.71±1.32 days. Clutch frequency in a nesting season was calculated as =1.71±1.6 times per female and season. Estimated number of nesting females per year varied from =373±12.5 females in 2001 to =1 669±56.1 females in 2008 (ANOVA F (5.6df)=89.42, p<0.0001); with a positive and significant trend (r=0.842, p=0.036). Results show that nesting females numbers are increasing. We suggest that the protection of the nesting area for more than 30 years, has contributed with this population increase. Rev. Biol. Trp. 60 (2): 745-758. Epub 2012 June 01.
Isla de Aves, una isla a 650km de La Guaira, Venezuela, protegida como Refugio de Fauna Silvestre, constituye el segundo sitio de mayor anidación de la tortuga verde (Chelonia mydas) (Linnaeus 1758) en el Caribe. El seguimiento de la población comenzó en 1972 y de manera más continua desde 1978. Los datos históricos indican que la captura de hembras en la isla, afectó severamente la población hasta 1978, cuando fue construida una base científico-naval. Durante las temporadas de anidación entre 2001-2008 con excepción de 2003 y 2004, las hembras fueron marcadas con placas metálicas y medidas. Asimismo, se muestreó durante 458 noches, en donde se observaron 5 154 eventos, con un máximo de 53 por noche. Los posibles eventos no observados fueron calculados ajustando la distribución temporal de eventos observados a una curva normal. El total de eventos estimados varió de =637.1±106.6 en 2001 a =2 853±42.5 en 2008 (ANOVA F(6.5gl)=60.37, p<0.0001). El intervalo entre reanidaciones fue de =10.7±1.32 días. La frecuencia de anidación se calculó en =1.71±1.6 veces por hembra. El número de hembras estimadas varió entre =373±12.5 para 2001 y =1 669±56.1 para 2008 (ANOVA F(5.6gl)=89.42, p<0.0001). La tendencia es significativa (r=0.842, p=0.036). Los resultados indican que el número de hembras que anidan en Isla de Aves ha aumentado, y se sugiere que más de 30 años de protección del área de reproducción está resultando en un creciente número de hembras.
