鳄蜥的食物识别机制

鳄蜥(Shinisaurus crocodilurus)食物识别机制的研究,对进一步了解鳄蜥的捕食行为和生态学习性有重要意义。使用棉棒分别沾上去离子水、香水、黄粉虫(Tenebriomolitor L.)和蚯蚓(Pheretima sp.)的气味(蚯蚓和黄粉虫处死后绞碎以便于棉花棒蘸上),观察11只鳄蜥对4种化学刺激的反应,每个个体对每种刺激均进行24次实验重复。实验结果显示：鳄蜥对4种刺激均有反应,对黄粉虫和蚯蚓刺激的舔舌次数显著高于香水和去离子水的舔舌次数(Wilcoxon test,所有P<0.001),表明鳄蜥能检测以及识别控制刺激和食物刺激。再又对鳄蜥进行4种处理实验：(A)空白对照;(B)蚯蚓气味;(C)密封着的活蚯蚓;(D)活蚯蚓。每个个体每种处理均进行5次实验。结果显示：鳄蜥在不同处理下的行为持续时间、探究频次和攻击频次有显著差异(Friedman test,所有P<0.001)。鳄蜥在仅有视觉刺激出现的处理C以及既有化学刺激又有视觉刺激的处理D比仅有化学刺激的处理B在持续时间、探究频次和攻击频次上显著要高（所有P<0.001）。在无视觉刺激的条件下,鳄蜥在处理B的行为持续时间以及探究频次均显著高于处理A 的（所有P<0.001）;而在视觉信息相同的条件下,鳄蜥在处理D中仅行为持续时间显著高于处理C（Z=3.95, P<0.001）,而探究频次以及攻击频次无显著差异（前者Z=1.53, P=0.13;后者Z=1.10, P=0.27）。结果表明鳄蜥主要利用视觉捕食,化学感觉有辅助作用。鳄蜥这种食物识别机制可能与捕食模式和种系发生有关,也可能受食物的影响。     

Estimating demographics of the Nile crocodile (Crocodylus niloticus Laurenti) in the panhandle region of the Okavango Delta,Botswana

The population status of the Nile crocodile (Crocodylus niloticus Laurenti) in the panhandle region of the Okavango Delta, Botswana, was assessed using mark–recapture and spotlight survey techniques following a decline because of commercial utilization. A total of 1717 individuals, ranging from 136 to 2780 mm in Snout Vent Length, were captured over a 4‐year period. Eighty‐one per cent of young juveniles encountered were successfully captured, representing 59.3% of total captures and 75% of recaptures. A Bayesian technique was used to estimate the number of young juveniles, and these estimates were then extrapolated for the other size classes. Survival and recapture analyses highlighted individual size‐dependent increases in wariness and survival. The total annual population was estimated to be 2570 ± 151.06 individuals, with an adult population of 649.2 individuals, including 364 females. We suggest that the harvest of breeding animals for commercial purposes should be halted until population recovery in this region is established.     

Molecular assessment of the genetic integrity,distinctiveness and phylogeographic context of the Saltwater crocodile (<Emphasis Type="Italic">Crocodylus porosus</Emphasis>) on Palau

The saltwater crocodile (Crocodylus porosus) is the largest and most broadly distributed crocodilian species, and thus is of special conservation and economic interest. Similar to other parts of its range throughout the Indo-Pacific, C. porosus distributed in the Republic of Palau have experienced a severe population decline over the past century primarily due to commercial hunting and eradication campaigns. In addition, several thousand crocodiles of undocumented species and origin were imported into Palau during the 1930’s for commercial farming purposes, potentially polluting the gene pool of the endemic saltwater crocodiles. Analysis of 39 individuals collected throughout the Republic of Palau revealed a single mitochondrial DNA control region haplotype shared by populations sampled in Sulawesi, Borneo and Australia. The mtDNA results, in combination with microsatellite genotypic data at six loci, detected no evidence for inter-specific hybridization between endemic Palauan C. porosus and potentially introduced Crocodylus species. There was no evidence for a genetic bottleneck in the Palauan population, however an excess of rare alleles was identified, indirectly suggesting a recent history of admixture potentially linked to introductions of non-native C. porosus. Following from these findings, Palauan C. porosus should be included in the single ESU previously established for all saltwater crocodiles given the recovery of a fixed, but geographically widespread haplotype. Although Palauan C. porosus exhibited significant genetic differentiation relative to all other sampled populations, it’s delineation as a distinct management unit is precluded at the present time by evidence that the genetic integrity of the population may have been compromised by the introduction of non-native saltwater crocodiles.     

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

Endangered species are often characterized by low genetic diversity and it is imperative for conservation efforts to incorporate the knowledge obtained from genetic studies for effective management. However, despite the promise of technological advances in sequencing, application of genome‐wide data to endangered populations remains uncommon. In the present study we pursued a holistic conservation‐genomic approach to inform a field‐based management programme of a Critically Endangered species, the Siamese crocodile Crocodylus siamensis. Using thousands of single nucleotide polymorphisms from throughout the genome, we revealed signals of introgression from two other crocodile species within our sample of both wild and captive‐bred Siamese crocodiles from Cambodia. Our genetic screening of the Siamese crocodiles resulted in the subsequent re‐introduction of 12 individuals into the wild as well as the selection of four individuals for captive breeding programmes. Comparison of intraspecific genetic diversity revealed an alarmingly low contemporary effective population size in the wild (<50) with evidence of a recent bottleneck around Tonle Sap Lake. We also projected a probable future extinction in the wild (within fewer than five generations) in this population in the absence of re‐introduction efforts. However, an increase in the number of potential breeders through re‐introductions, including the one resulting from this project, could counter this trend. Our results have been implemented in ongoing re‐introduction and captive breeding programmes, with major implications for the conservation management of Siamese crocodiles, and provide a blueprint for the rescue effort of other “terminally ill” populations of critically endangered species.     

Nesting Phenology and Clutch Characteristics of Captive Siamese Crocodiles (Crocodylus siamensis) in Cambodia

The Siamese crocodile (Crocodylus siamensis) is considered one of the least studied and most critically endangered crocodilians in the world. Although few wild populations remain, more than 700,000 C. siamensis are held on commercial crocodile farms in Southeast Asia. Despite conservation concerns, many aspects of C. siamensis life history remain poorly known, particularly with regards to its reproductive biology. We studied nesting phenology, clutch characteristics, and other aspects of C. siamensis reproductive biology on crocodile farms in Cambodia during 2000 and 2001. Oviposition among captive crocodiles began in February and continued into early June. The mean (±1 SD) oviposition date based on pooled data from 2000 and 2001 was 5 April ± 24 days. Mean oviposition date differed significantly between 2000 and 2001, possibly as a result of annual variability among nesting cues. The mean incubation period was 72 ± 3 days and eggs hatched from 5 May to 18 August. Mean clutch size (25.0 ± 8.8 eggs; n = 183) differed significantly between years, possibly resulting from the >2.5‐fold increase in sample size during 2001. There was no correlation between clutch size and oviposition date during either 2000 or 2001. A single female produced two clutches during 2001, complimenting previous reports of double‐clutching among C. siamensis. The mean length and width of 515 eggs were 78.2 ± 4.9 and 48.1 ± 2.5 mm, respectively; mean egg mass was 90.8 ± 16.5 g (n = 471). One unpipped egg contained a set of twins. Zoo Biol 31:534‐545, 2012. © 2011 Wiley Periodicals, Inc.     

Dietary constraints of phytosaurian reptiles revealed by dental microwear textural analysis

Phytosaurs are a group of large, semi‐aquatic archosaurian reptiles from the Middle–Late Triassic. They have often been interpreted as carnivorous or piscivorous due to their large size, morphological similarity to extant crocodilians and preservation in fluvial, lacustrine and coastal deposits. However, these dietary hypotheses are difficult to test, meaning that phytosaur ecologies and their roles in Triassic food webs remain incompletely constrained. Here, we apply dental microwear textural analysis to the three‐dimensional sub‐micrometre scale tooth surface textures that form during food consumption to provide the first quantitative dietary constraints for five species of phytosaur. We furthermore explore the impacts of tooth position and cranial robustness on phytosaur microwear textures. We find subtle systematic texture differences between teeth from different positions along phytosaur tooth rows, which we interpret to be the result of different loading pressures experienced during food consumption, rather than functional partitioning of food processing along tooth rows. We find rougher microwear textures in morphologically robust taxa. This may be the result of seizing and processing larger prey items compared to those captured by gracile taxa, rather than dietary differences per se. We reveal relatively low dietary diversity between our study phytosaurs and that individual species show a lack of dietary specialization. Species are predominantly carnivorous and/or piscivorous, with two taxa exhibiting slight preferences for ‘harder’ invertebrates. Our results provide strong evidence for higher degrees of ecological convergence between phytosaurs and extant crocodilians than previously appreciated, furthering our understanding of the functioning and evolution of Triassic ecosystems.     

Obituary: Ron K. Pickerill (1947–2018)

Recently discovered tracks in alluvial sediments of the Late Paleocene Bullion Creek Formation of western North Dakota have been identified as belonging to the large eusuchian crocodile Borealosuchus formidabilis and an associated small arthropod. They are described as two new ichnotaxa. The first of these, Borealosuchipus hanksi igen. et isp. nov., is based on a partly complete trackway having fore- and hind-footprints as well as body marks preserved in hyporelief. These tracks are directly associated with numerous body fossils including articulated bones which provide strong implications for their probable origin. The second specimen, Koupichnium pentapodus isp. nov., is founded on a trackway of a small invertebrate in which a series of five pairs of footprints are arranged along a midline drag mark which is continuous throughout the length of its trackway. This trackway shares features with other fossils as well as living arthropod trackways in which four small feet and a larger posterior hind “pusher” foot are present. The two described new ichnotaxa represent the first recognized tracks from the Wannagan Creek local fauna.     

Reproductive dynamics of a tropical freshwater crocodilian: Morelet's crocodile in northern Belize

Morelet's crocodile Crocodylus moreletii has not been well-studied and many aspects of its life history are unknown. In particular there is a notable paucity of information on nesting and reproductive ecology. We studied the nesting ecology of Morelet's crocodile in northern Belize from 1992 through 1995. Nesting occurs at the onset of the wet season in mid-June and continues through mid-July (mean oviposition date =1 July±10 days). Eggs hatch from mid-August through mid- to late September. Nesting effort at our primary study site remained relatively constant during 1992, 1993 and 1995, but nearly doubled in 1994; this appeared to reflect a regional trend. Natural and man-made islands are heavily used as nesting sites. Nesting success in 1993 and 1994 was consistently higher on natural islands when compared with man-made islands or shoreline sites. Nest losses were primarily due to flooding and raccoon Procyon lotor predation. Losses from predation were greatest in 1994 when unseasonably low water levels facilitated predator access to nests. Females probably reach sexual maturity in 7–8 years after attaining a total length of 150 cm. Mean clutch size (25.0±7.6; range=9–42; n =73) did not differ among years. Mean clutch size, egg width (EW), egg length, egg mass (EM) and clutch mass were positively correlated with female snout–vent length (SVL). Mean EW was the best predictor of female SVL. A partial correlation analysis of egg and clutch attributes found that independent of female SVL, EM increases with increasing clutch size.     

Crocodile farming and conservation,the example of Zimbabwe

Crocodile farming is an important and lucrative activity in Zimbabwe which provides meat for human consumption and skins for the luxury leather industry. Because it gives an economic value to this otherwise unfriendly animal, farming crocodiles has a positive side effect on the conservation of this species in the wild. This paper gives an overview of the crocodile industry in Zimbabwe.