A newt does not change its spots: using pattern mapping for the identification of individuals in large populations of newt species

Abstract

The correct identification of individuals is a requirement of capture‐mark‐recapture (CMR) methods, and it is commonly achieved by applying artificial marks or by mutilation of study‐animals. An alternative, non‐invasive method to identify individuals is to utilize the patterns of their natural body markings. However, the use of pattern mapping is not yet widespread, mainly because it is considered time consuming, particularly in large populations and/or long‐term CMR studies. Here we explore the use of pattern mapping for the identification of adult individuals in the alpine (Ichthyosaura alpestris) and smooth (Lissotriton vulgaris) newts (Amphibia, Salamandridae), using the freely available, open‐source software Wild‐ID. Our photographic datasets comprised nearly 4000 captured animals’ images, taken during a 3‐year period. The spot patterns of individual newts of both species did not change through time, and were sufficiently varied to allow their individual identification, even in the larger datasets. The pattern‐recognition algorithm of Wild‐ID was highly successful in identifying individual newts in both species. Our findings indicate that pattern mapping can be successfully employed for the identification of individuals in large populations of a broad range of animals that exhibit natural markings. The significance of pattern‐mapping is accentuated in CMR studies that aim in obtaining long‐term information on the demography and population dynamics of species of conservation interest, such as many amphibians facing population declines.

Ontogenetic changes in spot configuration (numbers, circularity, size and asymmetry) and lateral line in Neurergus microspilotus (Caudata: Salamandridae)

“…toe or scale clipping or tipping) of animals (Mettouris et al . ). Some of these invasive techniques may induce stress and influence the survival and/or behaviour of the target animal (Langkilde and Shine ; Antwis et al .…”

“…An alternative, non‐invasive method to identify individuals is to utilize their natural body markings, such as pigmentation pattern (stripes, spots or blotches; Mettouris et al . ). Pigmentation pattern mapping and analysis has been widely used for individual identification of different amphibian species (Carafa and Biondi ; Gamble et al .…”

“…; Mettouris et al . ), in many cases by manual or digital comparison of photographs with a reference photographic collection of individual colour patterns (Waye ).…”

“…Individual identification of animals is fundamental for answering several biological questions related to demographic, reproductive or ethological aspects, as for evaluation of survival rate, migrations and growth rate (Cove & Spínola, 2013;Williams, Nichols, & Conroy, 2002). Individual identification is commonly achieved by applying artificial marks (e.g., PIT-tags, visible implant elastomers, bands, tattoos) or by removing small parts (e.g., toe or scale clipping or tipping) of animals (Mettouris, Megremis, & Giokas, 2016). Some of these invasive techniques may induce stress and influence the survival and/or behaviour of the target animal (Antwis, Garcia, Fidgett, & Preziosi, 2014;Langkilde & Shine, 2006) and are often expensive, particularly in longterm studies (Morrison, Yoshizaki, Nichols, & Bolger, 2011).…”

“…Some of these invasive techniques may induce stress and influence the survival and/or behaviour of the target animal (Antwis, Garcia, Fidgett, & Preziosi, 2014;Langkilde & Shine, 2006) and are often expensive, particularly in longterm studies (Morrison, Yoshizaki, Nichols, & Bolger, 2011). An alternative, non-invasive method to identify individuals is to utilize their natural body markings, such as pigmentation pattern (stripes, spots or blotches; Mettouris et al, 2016). Pigmentation pattern mapping and analysis have been widely used for individual identification of different amphibian species (Carafa & Biondi, 2004;Gamble, Ravela, & McGarigal, 2008;Kenyon, Phillott, & Alford, 2009;Mettouris et al, 2016;Sharifi, Naderi, & Hashemi, 2013), in many cases by manual or digital comparison of photographs with a reference photographic collection of individual colour patterns (Waye, 2013).…”