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Papers by Dimitris Margaritoulis

Research paper thumbnail of Marine turtles: recovery of extinct populations

Instituto Canario de Ciencias Marinas [ISBN 978-84-612-1021-3], 229 p., 2006

Research paper thumbnail of Identification of a Developmental Habitat of the Green Turtle in Lakonikos Bay , Greece

Research paper thumbnail of Microsatellite analyses show restricted male-mediated gene flow between Mediterranean rookeries for loggerhead turtles

Research paper thumbnail of Using multiple methods to link the loggerhead foraging populations in Amvrakikos gulf, Greece, to source nesting populations in the Mediterranean

Research paper thumbnail of Complex Population Structure of the Endangered Loggerhead Sea Turtle (Caretta Caretta) in the Mediterranean Sea Revealed by Nuclear and Mitochondrial Dna Markers

Research paper thumbnail of Sea turtles in the Mediterranean : Distribution, threats and conservation priorities

IUCN eBooks, 2010

The Mediterranean Sea is a virtually enclosed basin that is frequented by three sea turtle specie... more The Mediterranean Sea is a virtually enclosed basin that is frequented by three sea turtle species. In the last three decades the interest in sea turtles in the Mediterranean has continuously increased, motivated by a growing concern for these threatened animals. There has also been a great interest and need to develop adequate knowledge about their threats and about the biological and ecological parameters that are relevant for their conservation. However, the number of countries, the variety of languages and the number of people involved in the region represent intrinsic difficulties for the diffusion of information and for coordinating large-scale actions. This report approaches these challenges head-on, by providing information about turtle occurrence, threats, conservation status and perspectives for each country. It can also help to diffuse information about successful models and lessons that have been learned throughout the region, and ultimately promote and improve cooperation for conservation.

Research paper thumbnail of High frequency of multiple paternity in the largest rookery of Mediterranean loggerhead sea turtles

Molecular Ecology, Sep 1, 2007

Mating systems are a central component in the evolution of animal life histories and in conservat... more Mating systems are a central component in the evolution of animal life histories and in conservation genetics. The patterns of male reproductive skew and of paternal shares in batches of offspring, for example, affect genetic effective population size. A prominent characteristic of mating systems of sea turtles seem to be a considerable intra-and interspecific variability in the degree of polyandry. Because of the difficulty of observing the mating behaviour of sea turtles directly in the open sea, genetic paternity analysis is particularly useful for gaining insights into this aspect of their reproductive behaviour. We investigated patterns of multiple paternity in clutches of loggerhead sea turtles in the largest Mediterranean rookery using four highly variable microsatellite loci. Furthermore, we tested for a relationship between the number of fathers detected in clutches and body size of females. More than one father was detected in the clutches of 14 out of 15 females, with two clutches revealing the contribution of at least five males. In more than half the cases, the contributions of different fathers to a clutch did not depart from equality. The number of detected fathers significantly increased with increasing female body size. This relationship indicates that males may prefer to mate with large, and therefore productive, females. Our results suggest that polyandry is likely to increase effective population size compared to a population in which females would mate with only one male; male reproductive contributions being equal.

Research paper thumbnail of Captures and Strandings of the Leatherback Sea Turtle, Dermochelys coriacea, in Greece (1982-1984)

Journal of Herpetology, Sep 1, 1986

Research paper thumbnail of Population Structure of Loggerhead Turtles (Caretta caretta) in the Northwestern Atlantic Ocean and Mediterranean Sea

Conservation Biology, Dec 1, 1993

Research paper thumbnail of Scalation Patterns of Loggerhead Turtles Nesting in Laganas Bay, Zakynthos Island, Greece

Research paper thumbnail of Growth rates and age at maturity of Mediterranean loggerhead sea turtles estimated from a single-population foraging ground

Marine Biology

In sea turtles, somatic growth rates and Age at Sexual Maturity (ASM) are important parameters fo... more In sea turtles, somatic growth rates and Age at Sexual Maturity (ASM) are important parameters for investigating population dynamics. Moreover, ASM informs on the time lag needed to observe the effects of past environmental variables, threats and conservation measures acting at nesting beaches on future numbers of clutches or nesting females, that are the most monitored indices. Assessing ASM of mixed populations that share the same foraging areas is difficult, as in the case of the Mediterranean Sea that is frequented by turtles originating from both the Mediterranean and the Atlantic. Here we investigated growth rates of loggerhead sea turtles (Caretta caretta) foraging in the Adriatic Sea, known to be frequented only by individuals of Mediterranean origin. Capture–mark–recapture records of 79 turtles provided growth rates ranging from – 1.1 to 9.6 cm yr−1 which were analyzed through Generalized Additive Models. When integrated with previous data on growth rates in the first years...

Research paper thumbnail of Spatial ecology of loggerhead turtles: Insights from stable isotope markers and satellite telemetry

Diversity and Distributions, 2020

AimUsing a combination of satellite telemetry and stable isotope analysis (SIA), our aim was to i... more AimUsing a combination of satellite telemetry and stable isotope analysis (SIA), our aim was to identify foraging grounds of loggerhead turtles (Caretta caretta) at important rookeries in the Mediterranean, examine foraging ground fidelity, and across 25 years determine the proportion of nesting females recruiting from each foraging region to a major rookery in Cyprus.LocationMediterranean Sea.MethodsBetween 1993 and 2018, we investigated the spatial ecology of loggerhead turtles from rookeries in Cyprus and Greece using satellite telemetry (n = 55 adults) and SIA of three elements (n = 296).ResultsSatellite telemetry from both rookeries revealed the main foraging areas as the Adriatic region (Cyprus: 4% of individuals, Greece: 55%), Tunisian Plateau (Cyprus: 16%, Greece: 40%) and the eastern Mediterranean (Cyprus: 80%, Greece: 5%). Combining satellite telemetry and SIA allowed 64% of all nesting females to be assigned to; the Adriatic region (Cyprus: 2%, Greece: 38.5%), Tunisian Pl...

Research paper thumbnail of Philopatry in loggerhead turtles Caretta caretta: beyond the gender paradigm

Marine Ecology Progress Series, 2018

Marine turtles have been traditionally considered model organisms to study sexbiased behaviour an... more Marine turtles have been traditionally considered model organisms to study sexbiased behaviour and dispersal. Although female philopatry has been identified in the loggerhead turtle, with adult females returning to specific locations to nest, studies on the philopatry and breeding migrations of males remain limited. In this study we analysed 152 hatchlings using 15 microsatellite markers. Each individual came from a different nest from samples taken at 8 nesting grounds in the Mediterranean. Our results revealed the existence of 5 genetically differentiated units, mostly due to restricted gene flow for both sexes. This supports existing satellite tracking studies that suggest that mating occurs close to nesting grounds in this region. The 5 management units identified within the Mediterranean included nesting grounds from (1) Libya and Cyprus, (2) Israel, (3) Lebanon, (4) Turkey and (5) Greece. The genetic similarity between distant nesting areas (i.e. Libya and Cyprus) suggests the presence of a more complex pattern of breeding behaviour. Three possible hypotheses, that remain to be tested in future studies, could explain this result: (1) mating might take place in common foraging grounds; (2) mating could occur en route while migrating to/from the breeding grounds; or (3) recent colonisation events could connect the 2 nesting grounds. Overall, our work suggests that widespread male-mediated gene flow between loggerhead nesting grounds is likely to have been previously overstated although opportunistic breeding patterns might connect some widely separated areas.

Research paper thumbnail of Mediterranean sea turtles: current knowledge and priorities for conservation and research

Endangered Species Research, 2018

Research paper thumbnail of Linking loggerhead locations: using multiple methods to determine the origin of sea turtles in feeding grounds

Marine biology, 2017

Many marine megavertebrate taxa, including sea turtles, disperse widely from their hatching or bi... more Many marine megavertebrate taxa, including sea turtles, disperse widely from their hatching or birthing locations but display natal homing as adults. We used flipper tagging, satellite tracking and genetics to identify the origin of loggerhead turtles living in Amvrakikos Gulf, Greece. This location has been identified as hosting regionally important numbers of large-juvenile to adult sized turtles that display long-term residency and/or association to the area, and also presents a male biased sex ratio for adults. A total of 20 individuals were linked to nesting areas in Greece through flipper tagging and satellite telemetry, with the majority (16) associated with Zakynthos Island. One additional female was tracked from Amvrakikos Gulf to Turkey where she likely nested. Mitochondrial DNA mixed stock analyses of turtles captured in Amvrakikos Gulf (n = 95) indicated 82% of individuals originated from Greek nesting stocks, mainly from Zakynthos Island (63%), with lesser contributions...

Research paper thumbnail of Changepoint analysis: a new approach for revealing animal movements and behaviors from satellite telemetry data

Research paper thumbnail of The effect of invertebrate infestation and its correlation with loggerhead turtle (Caretta caretta) nest success in Laganas Bay, Zakynthos, Greece

Research paper thumbnail of Fisheries interactions with marine turtles

Pages 279-286 in State of Hellenic Fisheries (C. Papaconstantinou, A. Zenetos,V. Vassilopoulou & G. Tserpes (Eds), Hellenic Centre for Marine Research Publ., 466 pp., 2007

Research paper thumbnail of Differences in size and reproductive output of loggerhead turtles Caretta caretta nesting in the eastern Mediterranean Sea are linked to foraging site

Marine Ecology Progress Series, 2015

Research paper thumbnail of The Inter-Nesting Interval of Zakynthos Loggerheads

Adaptations to Terrestrial Environments, 1983

Although sea turtles live almost all their lives in the sea, they depend on the terrestrial habit... more Although sea turtles live almost all their lives in the sea, they depend on the terrestrial habitat for reproduction. Female turtles come on land for short periods to lay their eggs and hatchlings emerging from nests in the sand walk briefly on land before entering (probably forever if they are males) the marine habitat. Nesting occurs on specific beaches, the “nesting beaches” or “rookeries”, where the majority of the female population converges during the nesting season.

Research paper thumbnail of Marine turtles: recovery of extinct populations

Instituto Canario de Ciencias Marinas [ISBN 978-84-612-1021-3], 229 p., 2006

Research paper thumbnail of Identification of a Developmental Habitat of the Green Turtle in Lakonikos Bay , Greece

Research paper thumbnail of Microsatellite analyses show restricted male-mediated gene flow between Mediterranean rookeries for loggerhead turtles

Research paper thumbnail of Using multiple methods to link the loggerhead foraging populations in Amvrakikos gulf, Greece, to source nesting populations in the Mediterranean

Research paper thumbnail of Complex Population Structure of the Endangered Loggerhead Sea Turtle (Caretta Caretta) in the Mediterranean Sea Revealed by Nuclear and Mitochondrial Dna Markers

Research paper thumbnail of Sea turtles in the Mediterranean : Distribution, threats and conservation priorities

IUCN eBooks, 2010

The Mediterranean Sea is a virtually enclosed basin that is frequented by three sea turtle specie... more The Mediterranean Sea is a virtually enclosed basin that is frequented by three sea turtle species. In the last three decades the interest in sea turtles in the Mediterranean has continuously increased, motivated by a growing concern for these threatened animals. There has also been a great interest and need to develop adequate knowledge about their threats and about the biological and ecological parameters that are relevant for their conservation. However, the number of countries, the variety of languages and the number of people involved in the region represent intrinsic difficulties for the diffusion of information and for coordinating large-scale actions. This report approaches these challenges head-on, by providing information about turtle occurrence, threats, conservation status and perspectives for each country. It can also help to diffuse information about successful models and lessons that have been learned throughout the region, and ultimately promote and improve cooperation for conservation.

Research paper thumbnail of High frequency of multiple paternity in the largest rookery of Mediterranean loggerhead sea turtles

Molecular Ecology, Sep 1, 2007

Mating systems are a central component in the evolution of animal life histories and in conservat... more Mating systems are a central component in the evolution of animal life histories and in conservation genetics. The patterns of male reproductive skew and of paternal shares in batches of offspring, for example, affect genetic effective population size. A prominent characteristic of mating systems of sea turtles seem to be a considerable intra-and interspecific variability in the degree of polyandry. Because of the difficulty of observing the mating behaviour of sea turtles directly in the open sea, genetic paternity analysis is particularly useful for gaining insights into this aspect of their reproductive behaviour. We investigated patterns of multiple paternity in clutches of loggerhead sea turtles in the largest Mediterranean rookery using four highly variable microsatellite loci. Furthermore, we tested for a relationship between the number of fathers detected in clutches and body size of females. More than one father was detected in the clutches of 14 out of 15 females, with two clutches revealing the contribution of at least five males. In more than half the cases, the contributions of different fathers to a clutch did not depart from equality. The number of detected fathers significantly increased with increasing female body size. This relationship indicates that males may prefer to mate with large, and therefore productive, females. Our results suggest that polyandry is likely to increase effective population size compared to a population in which females would mate with only one male; male reproductive contributions being equal.

Research paper thumbnail of Captures and Strandings of the Leatherback Sea Turtle, Dermochelys coriacea, in Greece (1982-1984)

Journal of Herpetology, Sep 1, 1986

Research paper thumbnail of Population Structure of Loggerhead Turtles (Caretta caretta) in the Northwestern Atlantic Ocean and Mediterranean Sea

Conservation Biology, Dec 1, 1993

Research paper thumbnail of Scalation Patterns of Loggerhead Turtles Nesting in Laganas Bay, Zakynthos Island, Greece

Research paper thumbnail of Growth rates and age at maturity of Mediterranean loggerhead sea turtles estimated from a single-population foraging ground

Marine Biology

In sea turtles, somatic growth rates and Age at Sexual Maturity (ASM) are important parameters fo... more In sea turtles, somatic growth rates and Age at Sexual Maturity (ASM) are important parameters for investigating population dynamics. Moreover, ASM informs on the time lag needed to observe the effects of past environmental variables, threats and conservation measures acting at nesting beaches on future numbers of clutches or nesting females, that are the most monitored indices. Assessing ASM of mixed populations that share the same foraging areas is difficult, as in the case of the Mediterranean Sea that is frequented by turtles originating from both the Mediterranean and the Atlantic. Here we investigated growth rates of loggerhead sea turtles (Caretta caretta) foraging in the Adriatic Sea, known to be frequented only by individuals of Mediterranean origin. Capture–mark–recapture records of 79 turtles provided growth rates ranging from – 1.1 to 9.6 cm yr−1 which were analyzed through Generalized Additive Models. When integrated with previous data on growth rates in the first years...

Research paper thumbnail of Spatial ecology of loggerhead turtles: Insights from stable isotope markers and satellite telemetry

Diversity and Distributions, 2020

AimUsing a combination of satellite telemetry and stable isotope analysis (SIA), our aim was to i... more AimUsing a combination of satellite telemetry and stable isotope analysis (SIA), our aim was to identify foraging grounds of loggerhead turtles (Caretta caretta) at important rookeries in the Mediterranean, examine foraging ground fidelity, and across 25 years determine the proportion of nesting females recruiting from each foraging region to a major rookery in Cyprus.LocationMediterranean Sea.MethodsBetween 1993 and 2018, we investigated the spatial ecology of loggerhead turtles from rookeries in Cyprus and Greece using satellite telemetry (n = 55 adults) and SIA of three elements (n = 296).ResultsSatellite telemetry from both rookeries revealed the main foraging areas as the Adriatic region (Cyprus: 4% of individuals, Greece: 55%), Tunisian Plateau (Cyprus: 16%, Greece: 40%) and the eastern Mediterranean (Cyprus: 80%, Greece: 5%). Combining satellite telemetry and SIA allowed 64% of all nesting females to be assigned to; the Adriatic region (Cyprus: 2%, Greece: 38.5%), Tunisian Pl...

Research paper thumbnail of Philopatry in loggerhead turtles Caretta caretta: beyond the gender paradigm

Marine Ecology Progress Series, 2018

Marine turtles have been traditionally considered model organisms to study sexbiased behaviour an... more Marine turtles have been traditionally considered model organisms to study sexbiased behaviour and dispersal. Although female philopatry has been identified in the loggerhead turtle, with adult females returning to specific locations to nest, studies on the philopatry and breeding migrations of males remain limited. In this study we analysed 152 hatchlings using 15 microsatellite markers. Each individual came from a different nest from samples taken at 8 nesting grounds in the Mediterranean. Our results revealed the existence of 5 genetically differentiated units, mostly due to restricted gene flow for both sexes. This supports existing satellite tracking studies that suggest that mating occurs close to nesting grounds in this region. The 5 management units identified within the Mediterranean included nesting grounds from (1) Libya and Cyprus, (2) Israel, (3) Lebanon, (4) Turkey and (5) Greece. The genetic similarity between distant nesting areas (i.e. Libya and Cyprus) suggests the presence of a more complex pattern of breeding behaviour. Three possible hypotheses, that remain to be tested in future studies, could explain this result: (1) mating might take place in common foraging grounds; (2) mating could occur en route while migrating to/from the breeding grounds; or (3) recent colonisation events could connect the 2 nesting grounds. Overall, our work suggests that widespread male-mediated gene flow between loggerhead nesting grounds is likely to have been previously overstated although opportunistic breeding patterns might connect some widely separated areas.

Research paper thumbnail of Mediterranean sea turtles: current knowledge and priorities for conservation and research

Endangered Species Research, 2018

Research paper thumbnail of Linking loggerhead locations: using multiple methods to determine the origin of sea turtles in feeding grounds

Marine biology, 2017

Many marine megavertebrate taxa, including sea turtles, disperse widely from their hatching or bi... more Many marine megavertebrate taxa, including sea turtles, disperse widely from their hatching or birthing locations but display natal homing as adults. We used flipper tagging, satellite tracking and genetics to identify the origin of loggerhead turtles living in Amvrakikos Gulf, Greece. This location has been identified as hosting regionally important numbers of large-juvenile to adult sized turtles that display long-term residency and/or association to the area, and also presents a male biased sex ratio for adults. A total of 20 individuals were linked to nesting areas in Greece through flipper tagging and satellite telemetry, with the majority (16) associated with Zakynthos Island. One additional female was tracked from Amvrakikos Gulf to Turkey where she likely nested. Mitochondrial DNA mixed stock analyses of turtles captured in Amvrakikos Gulf (n = 95) indicated 82% of individuals originated from Greek nesting stocks, mainly from Zakynthos Island (63%), with lesser contributions...

Research paper thumbnail of Changepoint analysis: a new approach for revealing animal movements and behaviors from satellite telemetry data

Research paper thumbnail of The effect of invertebrate infestation and its correlation with loggerhead turtle (Caretta caretta) nest success in Laganas Bay, Zakynthos, Greece

Research paper thumbnail of Fisheries interactions with marine turtles

Pages 279-286 in State of Hellenic Fisheries (C. Papaconstantinou, A. Zenetos,V. Vassilopoulou & G. Tserpes (Eds), Hellenic Centre for Marine Research Publ., 466 pp., 2007

Research paper thumbnail of Differences in size and reproductive output of loggerhead turtles Caretta caretta nesting in the eastern Mediterranean Sea are linked to foraging site

Marine Ecology Progress Series, 2015

Research paper thumbnail of The Inter-Nesting Interval of Zakynthos Loggerheads

Adaptations to Terrestrial Environments, 1983

Although sea turtles live almost all their lives in the sea, they depend on the terrestrial habit... more Although sea turtles live almost all their lives in the sea, they depend on the terrestrial habitat for reproduction. Female turtles come on land for short periods to lay their eggs and hatchlings emerging from nests in the sand walk briefly on land before entering (probably forever if they are males) the marine habitat. Nesting occurs on specific beaches, the “nesting beaches” or “rookeries”, where the majority of the female population converges during the nesting season.