Yolk removal generates hatching asynchrony in snake eggs

Fabien Aubret,Philippe J R Kok,Florent Bignon,Jérémie Souchet,Gaëlle Blanvillain,Alix Bouffet-Halle

doi:10.1038/s41598-017-03355-y

Abstract

Hatching synchrony is wide-spread amongst egg-laying species and is thought to enhance offspring survival, notably by diluting predation risks. Turtle and snake eggs were shown to achieve synchronous hatching by altering development rates (where less advanced eggs may accelerate development) or by hatching prematurely (where underdeveloped embryos hatch concurrently with full-term embryos). In Natricine snakes, smaller eggs tend to slow down metabolism throughout incubation in order to hatch synchronously with larger eggs. To explore the underlying mechanism of this phenomenon we experimentally manipulated six clutches, where half of the eggs were reduced in mass by removing 7.2% of yolk, and half were used as the control. The former experienced higher heart rates throughout the incubation period, hatched earlier and produced smaller hatchlings than the latter. This study supports the idea that developmental rates are related to egg mass in snake eggs and demonstrates that the relationship can be influenced by removing yolk after egg-laying. The shift in heart rates however occurred in the opposite direction to expected, with higher heart rates in yolk-removed eggs resulting in earlier hatching rather than lower heart rates resulting in synchronous hatching, warranting further research on the topic.

Highlights

Synchronised hatching, a form of environmentally cued hatching[1] (ECH), is widespread amongst organisms; including invertebrates[2], fishes[3], amphibians[4,5,6], crocodilians[7], squamates[8,9,10], turtles[11, 12] and birds[13, 14]
Experimental evidence[10, 12, 18, 25, 26] suggests that synchronous hatching may be generated via (i) the alteration of development rates, or (ii) premature hatching
To explore the inner mechanisms of hatching synchrony and the relationship between egg mass and metabolic rate, we collected clutches of the water snake Natrix maura: in each clutch, half of the eggs were reduced in mass by removing 7.2% of yolk using a syringe

Summary

Introduction

Synchronised hatching, a form of environmentally cued hatching[1] (ECH), is widespread amongst organisms; including invertebrates[2], fishes[3], amphibians[4,5,6], crocodilians[7], squamates (snakes and lizards)[8,9,10], turtles[11, 12] and birds[13, 14]. Mechanisms that promote hatching synchrony are poorly understood[11] In both avian and non-avian reptiles[12, 17,18,19,20], communication avenues amongst embryos or between embryos and parents may involve chemical cues, vibrations (including heart beats), acoustic cues and hypoxia[11]. Embryo communication in reptiles was shown to promote hatching synchrony primarily via metabolic compensation between more and less advanced eggs (in turtles[12, 18, 25]; and snakes26) or between large and smaller eggs (in snakes[10]).

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