''Lepidodactylus listeri'', also known commonly as Lister's gecko and the Christmas Island chained gecko, is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Gekkonidae Gekkonidae (the common geckos) is the largest family of geckos, containing over 950 described species in 62 genera. The Gekkonidae contain many of the most widespread gecko species, including house geckos (''Hemidactylus''), the tokay gecko (''Ge ...

. The species was

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

Christmas Island Christmas Island, officially the Territory of Christmas Island, is an States and territories of Australia#External territories, Australian external territory in the Indian Ocean comprising the island of the same name. It is about south o ...

in the Indian Ocean. It is

extinct in the wild A species that is extinct in the wild (EW) is one that has been categorized by the International Union for Conservation of Nature as only consisting of living members kept in captivity or as a naturalized population outside its historic range ...

Geographic range

''L. listeri'' was endemic to Christmas Island.

Etymology

Both the

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

, ''listeri'', and one of the common names, Lister's gecko, are in honour of British naturalist

Joseph Jackson Lister Joseph Jackson Lister FRS FRMS (11 January 1786 – 24 October 1869) was an English opticist and physicist best known for being the father of Joseph Lister, 1st Baron Lister. Life In 1705, Thomas Lister, a farmer and maltster, of Bingley, Yo ...

. xiii + 296 pp. (''Lepidodactylus listeri'', p. 159).

Description

Lister's gecko is a brown lizard growing to a snout-to-vent length (SVL) of . It has a broad, pale fawn/grey

vertebral Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

stripe which expands to cover the top of the head and matches the colour and pattern of the tail. It has a whitish belly. The body is covered with small, smooth scales. 808 pp.

Habitat

''L. listeri'' was most abundant in primary

rainforest Rainforests are forests characterized by a closed and continuous tree Canopy (biology), canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforests can be generally classified as tropi ...

on the plateau, but also occurred in disturbed secondary

forest A forest is an ecosystem characterized by a dense ecological community, community of trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, ...

growth. It was absent from mined areas on the island.Cogger HG, Sadlier RA (1999). ''The terrestrial reptiles of Christmas Island – a reappraisal of their status''. Sydney: Australian Museum.

Behaviour

''L. listeri'' is

nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

and

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...

. During daylight hours, it shelters under bark.

Reproduction

''L. listeri'' is

oviparous Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings kno ...

Clutch A clutch is a mechanical device that allows an output shaft to be disconnected from a rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does th ...

size is two eggs.

Evolutionary relationships

The closest relatives of ''L. listeri'' are species of ''

Lepidodactylus ''Lepidodactylus'' is a large genus of geckos, commonly known as scaly-toed geckos and closely related to house geckos or Gehyra, dtellas. Geographic range Species in the genus ''Lepidodactylus'' are found from Southeast Asia to Indo-Australi ...

'' belonging to the '' lugubris''

species group In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

, native to the Mollucas and the

Philippines The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...

, with the estimated divergence between ''L. listeri'' and the ''lugubris'' group taking place around 26 million years ago. Unlike '' L. lugubris'', which can be

triploid Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...

and reproduce through

parthenogenesis Parthenogenesis (; from the Greek + ) is a natural form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization. In animals, parthenogenesis means the development of an embryo from an unfertiliz ...

, ''L. listeri'' is a

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

, sexually reproducing species.

Decline

''L. listeri'' was considered to be generally common in 1979, and was widespread across the island, but population declines were noted by researchers starting in 1998. Further decline was noted in 2004 and in 2008. By 2009, it was recognized that the species was in imminent danger of extinction, and a captive breeding program was established. The last record of ''L. listeri'' in its native habitat on Christmas Island was in October 2012. The decline of ''L. listeri'' was concurrent with the widespread decline of most endemic mammal and reptile species on Christmas Island, and it is considered that this decline was the result of a common cause, or a combination thereof. The causes of this decline are not well understood. However it is believed that predation by introduced species, particularly the wolf snake ('' Lycodon capucinus''), may have played a significant role. The wolf snake was introduced around 1982, which is within the timeframe that the population decline began.

Conservation efforts

Prior to the extirpation of this species from Christmas Island, 43 individuals were taken into captivity, starting in August 2009, in order to establish a breeding population. This proved successful with a total population of over 1,500 individuals as of July 2022. However, reintroduction is unlikely to occur in the near future. Invasive threats are not yet controlled on Christmas Island, and assisted colonization is not yet feasible due to widespread gecko '' L. lugubris,'' which has an unknown conservation status.

Genome

The genome of ''L. listeri'' was sequenced in 2022 (along with the Christmas Island blue-tailed skink), making it one of the earliest chromosome-level gecko genomes. The genome was genetically diverse, reflective of large historical population sizes. Despite the captive population being founded from just 43 individuals, there was not evidence of inbreeding in the genome.