Research Article |
Corresponding author: Mariana Chuliver ( marianachp@yahoo.com.ar ) Academic editor: Uwe Fritz
© 2023 Mariana Chuliver, Agustín Scanferla.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Chuliver M, Scanferla A (2023) Novel type of egg-clustering in threadsnakes (Serpentes: Leptotyphlopidae). Vertebrate Zoology 73: 691-696. https://doi.org/10.3897/vz.73.e108402
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Abstract
Snakes lay their eggs in clutches of different size, which are usually attached to each other forming a cluster. Egg-clustering is a widespread phenomenon across alethinophidian snakes, mostly recorded in Pythonoidea and caenophidian clades. Here we report a new type of egg-clustering for threadsnakes (Leptotyphlopidae) that departs from the alethinophidian type. We found that females of Epictia australis and Leptotyphlops sylvicolus lay their eggs connected to each other through a filament, and we dubbed it ‘string-egg clustering’. The histomorphology of the filament linking the eggs in E. australis showed an outer calcareous layer underlain by a thick layer of collagen fibers, demonstrating that it is an integral part of the eggshell formed during its deposition process in the oviduct. String egg-clustering seems to be present only among species belonging to both subfamilies of threadsnakes, Epictinae and Leptotyphlopinae. Egg-clustering in alethinophidians has been demonstrated to have several advantages for embryo development and post-hatching survival, including fixing the position of the embryo within the egg, protection against predators, and embryo-to-embryo communication. The presence of a filament connecting the eggs in leptotyphlopid species might be relevant for maintaining the position of the embryo in the egg, to avoid the dispersion of the egg in the nesting site, and potentially for the transmission of physical cues. Thus, we hypothesize that the string-egg clustering constitutes an advantageous reproductive trait among threadsnakes.
Blindsnakes, egg clutch, eggshell histology, Epictia australis, Leptotyphlops sylvicolus, string egg-clustering
Oviparous squamate reptiles lay shelled eggs in clutches of different size, which develop together in nests of variable complexity (
Thus far, oviposition and/or structure of the eggshell have been documented across alethinophidian snakes, mostly in Pythonoidea and caenophidian clades (
Herein, we documented the presence of a novel type of egg-clustering for snakes in two species of the family Leptotyphlopidae: Epictia australis (Freiberg & Orejas-Miranda, 1968) and Leptotyphlops sylvicolus Broadley & Wallach, 1997. We also characterized the histomorphology of the eggshell of E. australis, and conducted an exhaustive bibliographic search on blindsnake reproduction. This allowed us (1) to determine the nature of the structure connecting the eggs, (2) to explore whether different types of egg-clustering were previously reported for other species, and (3) to test the hypothesis of the exclusiveness of the novel type of egg-clustering for the family Leptotyphlopidae.
A gravid female of the austral threadsnake Epictia australis was collected in Sierra de la Ventana region (38°12’21”S; 61°28’59”W) on 20 November 2022 (BA permit EX-2022-20466509-GDEBA-DSTAMDAGP). It was housed individually in a plastic container and kept in captivity in the laboratory. Soon after its capture, it laid five eggs, which were incubated in a plastic container at 27–30°C temperature using perlite substrate. Both the female and embryos were euthanized, preserved in an ethanol 70% solution, and deposited in the herpetological collection of Fundación Azara (CFA-RE 663). Additionally, a female of E. australis (CFA-RE 666) was dissected in order to observe oviductal eggs. Longitudinal (sagittal) serial sections of 6 μm thickness of a paraffin-embedded egg of E. australis were stained with hematoxylin–eosin (
A second gravid female of the forest threadsnake Leptotyphlops sylvicolus, was found below a stone in the Midmar Nature Reserve in KwaZulu-Natal (South Africa). The specimen was housed individually in a plastic container and then laid three eggs, which were photographed and measured before being left in the same place where the adult was found. All measurements were taken using a dial caliper (accuracy: 0.05 mm) with measurements given in millimeters.
Finally, we performed an exhaustive bibliographic survey on blindsnake reproduction (Table
Available information on clutch size and presence of egg clustering in blindsnake species.
Family | Species | Clutch size | Egg clustering | Source |
Typhlopidae | Afrotyphlops bibronii | 5 to 12 | No |
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Typhlopidae | Amerotyphlops brongersmianus | 4 | No |
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Typhlopidae | Amerotyphlops paucisquamus | 3 | No |
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Typhlopidae | Anilios nigrescens | 4 to 20 | No |
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Typhlopidae | Indotyphlops braminus | 3 | No |
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Typhlopidae | Letheobia acutirostrata | 6 | No |
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Leptotyphlopidae | Epictia australis | 5 | Yes | This work |
Leptotyphlopidae | Leptotyphlops sylvicolus | 3 | Yes | This work |
Leptotyphlopidae | Leptotyphlops scutifrons | 3 to 7 | Yes |
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Leptotyphlopidae | Leptotyphlops conjunctus | 3 | No |
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Leptotyphlopidae | Rena humilis | 4 | No |
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Leptotyphlopidae | Rena dulcis | 4 | No |
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Leptotyphlopidae | Myriopholis longicauda | 2 | No |
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Anomalepididae | Liotyphlops albirostris | 3 | No |
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The snout-vent length (SVL) of the gravid female of Epictia australis (CFA-RE 663) was 159 mm. The clutch had five eggs, each of which measured 15 mm (Fig.
The histomorphology of the eggshell of E. australis (Fig.
The compiled information on blindsnake reproduction showed that, in addition to the two species documented here, the filament was only mentioned for Leptotyphlops scutifrons (Peters, 1854) (Table
We documented a novel type of egg-clustering for two blindsnake species, dubbed here ‘string egg-clustering’. The results of this study agree with an anecdotal account, as the string egg-clustering type was mentioned by the African herpetologist William Roy Branch in his renowned field guide of southern African reptiles (
Based on its general structure, the eggshell of Epictia australis can be classified into the group of flexible-shelled eggs with little calcareous layer, as in most squamates (
The histological analysis demonstrates that the filament linking the eggs constitutes an extension of the fibrillar and calcareous layers of the eggshell, indicating that both the eggshell and the filament are formed by the same eggshelling process. In squamates, the deposition of the organic membrane of the eggshell begins once fertilization has occurred, from the shell glands located in the middle oviduct (
Historically, it has been assumed that rolling of the eggs of squamate reptiles during early phases of incubation may result in the death of the embryo, suggesting that eggs must be incubated in the position in which the female laid them. This hypothesis has recently been tested in snakes, demonstrating that egg turning did not significantly influence egg development, hatching success or hatchling phenotypes but decreases survival of postnatal individuals (
The type of egg-clustering reported here for threadsnakes contrasts with the egg-clustering described for alethinophidian snakes, where eggs are directly adhered to each other through extensive areas of their eggshells (Fig.
Different types of egg-clustering in snakes. A string egg-clustering of leptotyphlopid snakes represented by Leptotyphlops sylvicolus and its egg clutch (photo taken by Tyrone Ping), B contact egg-clustering of alethinophidian snakes represented by the egg clutch of the pythonid Morelia spilota (photo taken from https://www.bromiespythons.com/post/eggs-are-here).
Both authors were funded by Agencia Nacional de Promoción Científica y Técnica (PICT Serie A 2020-2443). We thank our South African colleague Tyrone Ping who generously provided valuable data and images of Leptotyphlops sylvicolus. We are also grateful to Sergio Bogan (Fundación Azara) for giving access to specimens in collections. Verónica Dorfman (Universidad Maimónides) kindly provided technical assistance with histological procedures. Appropriate protocols for the collection and handling of the specimens used in this study were followed. The manuscript also benefitted from reviews by two reviewers, and Krister Smith generously provided suggestions and help with English grammar.