High genetic diversity and demographic history of captive Siamese and Saltwater crocodiles suggest the first step toward the establishment of a breeding and reintroduction program in Thailand

Abstract

The Siamese crocodile (Crocodylus siamensis) and Saltwater crocodile (C. porosus) are two of the most endangered animals in Thailand. Their numbers have been reduced severely by hunting and habitat fragmentation. A reintroduction plan involving captive-bred populations that are used commercially is important and necessary as a conservation strategy to aid in the recovery of wild populations. Here, the genetic diversity and population structure of 69 individual crocodiles, mostly members of captive populations, were analyzed using both mitochondrial D-loop DNA and microsatellite markers. The overall haplotype diversity was 0.924–0.971 and the mean expected heterozygosity across 22 microsatellite loci was 0.578–0.701 for the two species. This agreed with the star-like shaped topology of the haplotype network, which suggests a high level of genetic diversity. The mean ratio of the number of alleles to the allelic range (M ratio) for the populations of both species was considerably lower than the threshold of 0.68, which was interpreted as indicative of a historical genetic bottleneck. Microsatellite markers provided evidence of introgression for three individual crocodiles, which suggest that hybridization might have occurred between C. siamensis and C. porosus. D-loop sequence analysis detected bi-directional hybridization between male and female individuals of the parent species. Therefore, identification of genetically non-hybrid and hybrid individuals is important for long-term conservation management. Relatedness values were low within the captive populations, which supported their genetic integrity and the viability of a breeding and reintroduction management plan. This work constitutes the first step in establishing an appropriate source population from a scientifically managed perspective for an in situ/ex situ conservation program and reintroduction of crocodile individuals to the wild in Thailand.

Predictive genetic plan for a captive population of the Chinese goral (Naemorhedus griseus) and prescriptive action for ex situ and in situ conservation management in Thailand

“…Management of Chinese goral populations is important to guarantee their long-term survival in natural environments. To increase the Chinese goral population size, a captive breeding program is the only viable option because the species is almost extinct in the wild [11][12][13]. In 1993, a Chinese goral population was established outside their natural habitat (ex situ) at Omkoi Wildlife Breeding Center in Chiang Mai (17˚28'14.8", 98˚26'51.2"), Thailand.…”

“…Maintenance of genetic diversity and demographic security are the primary goals for longterm conservation-population management. High genetic variation is the basis for adaptive evolution and survival and should be retained to promote the fitness of both individuals and the population [11][12][13]. By contrast, deleterious effects of inbreeding frequently occur in small captive populations, leading to decline of fitness and inbreeding depression [12,13].…”

Conservation genomics in the fight to help the recovery of the critically endangered Siamese crocodile Crocodylus siamensis

“…The wild population of Siamese crocodiles is thought to be less than 1,000 (Bezuijen et al, ; Ihlow et al, ). However, although over 1 million Siamese‐like crocodiles are known to reside in crocodile farms throughout Southeast Asia, their potential use for conservation and re‐introduction purposes has remained controversial, with their genomic purity in doubt (Daltry et al, ; Lapbenjakul et al, ; Sam et al, ; Simpson & Bezuijen, ). Decades of mixed pairings in captivity may have eroded the genomic purity of captive individuals to an unknown degree (Fitzsimmons et al, ; Sam et al, ).…”

“…Any efforts at Siamese crocodile conservation through captive breeding and re-introductions necessitate first a determination of the genomic purity of potential candidates for relocation (Fitzsimmons et al, 2002;Lapbenjakul et al, 2017;Sam et al, 2015), and second an assessment of the overall population-genomic diversity as well as genetic relatedness among them. In combination these measures can ensure a maximization of population-genomic diversity and a minimization of human-induced genetic introgression among individuals to be released into the wild (Lapbenjakul et al, 2017;Sam et al, 2015). In addition, an understanding of the genetic diversity and recent population history of wild populations of the F I G U R E 1 Map showing the distribution of the Siamese crocodile and sampling locations.…”

Development, characterization and determination of biological properties of crocodile hemoglobin (Crocodylus siamensis ) tablets

“…In this context, the Siamese crocodile ( Crocodylus siamensis ) may be regarded as a particularly attractive source for biologically active proteins, short peptides, and amino acids (Pakdeesuwan et al, ) as previous reports identified several proteins and peptides contained in crocodile blood to constitute the first line of innate immune defense protecting these animals against bacterial infection (Hoffman, Biscayne, Binah, & Tivan, ; Phosri et al, ). Although the Siamese crocodile is classified as critically endangered in the wild, the successful initiation of intensive breeding programs in Thailand aiming to conserve the species have created large captive populations in crocodile farms (Lapbenjakul et al, ). As a result, industrial crocodile farming in Thailand has experienced substantial growth in recent years to satisfy the increasing demand for crocodile‐based products, in particular meat and leather as the most valuable export commodities.…”