The dynamic eggs of the Phasmatodea and their apparent convergence with plants
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REVIEW
The dynamic eggs of the Phasmatodea and their apparent convergence with plants James C. O’Hanlon 1
&
Braxton R. Jones 2
&
Matthew W. Bulbert 2
Received: 9 April 2020 / Revised: 22 July 2020 / Accepted: 23 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The egg stages of animal life cycles are underappreciated in terms of their capacity for dispersal, protection, and biotic and abiotic interactions. Some of the most intriguing egg morphologies are seen in stick and leaf insects (Phasmatodea). Phasmids are charismatic insects, particularly due to their incredible camouflage, though a lesser-known fact is that their eggs are incredibly diverse in shape and structure, reflecting varying ecological niches. Perhaps most remarkable are those eggs which appear to resemble plant seeds in both their appearance and means of dispersal, such as via water and animal vectors. Numerous hypotheses surrounding the function of these egg morphologies and their apparent convergence with seeds have been proposed; however, empirical evidence remains lacking. Here, we present an initial synthesis of available evidence surrounding the ecology and dispersal strategies of phasmid eggs and weigh up the evidence for convergent evolution between phasmid eggs and seeds. In doing so, we highlight areas where further research is needed and discuss how the ecology of phasmid eggs may interplay with other aspects of phasmid ecology, distribution, and evolution. Keywords Dispersal . Stick insects . Seeds . Egg . Myrmecochory . Phoresy
Eggs as dynamic entities The tendency for behavioural and ecological research to focus on mature animals can overlook the majority of behavioural and ecological interactions that can occur. Juvenile stages of animal life histories—including nymphal, larval, and egg (or embryonic) stages—often make up the longest component of animal life cycles, yet their unique ecology may often be overlooked in favour of understanding the ecology and evolution of adult forms (Guerra-Grenier 2019). In the case of eggs, their immobility and inherent vulnerability imply that survival through the egg stage can be heavily dependent on the actions of the parent including oviposition site selection and adult defence (e.g. Montgomerie and Weatherhead 1988; Communicated by: José Eduardo Serrão * James C. O’Hanlon [email protected] 1
School of Environmental and Rural Science, University of New England, Armidale 2350, Australia
2
Department of Biological Sciences, Macquarie University, Balaclava Road, North Ryde, NSW 2109, Australia
Refsneider and Janzen 2010). Often though, the investment of parents in egg care, especially in insects, is limited (Wong et al. 2013). Thus, the eggs are left to defend themselves without the option of being able to flee. Eggs are far from being passive entities with selection favouring a broad range of abiotic and biotic interactions crucial for their survival. The colours and patterning of eggs, for example, may transmit visual signals that deter predators, may r
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