Aphids Playing Possum – Defensive or Mutualistic Response?
J Insect Behav
Aphids Playing Possum - Defensive or Mutualistic Response?
Aleksandra Bilska 0 1 2
Jacek Francikowski 0 1 2
Aleksandra Wyglenda 0 1 2
Adrian Masłowski 0 1 2
Natalia Kaszyca 0 1 2
Łukasz Depa 0 1 2
0 Department of Animal Physiology and Ecotoxicology, Faculty of Biology and Environmental Protection, University of Silesia , Bankowa 9, 40-007 Katowice , Poland
1 Students' Scientific Association of Zoologists BFauantycy
2 Department of Zoology, Faculty of Biology and Environmental Protection, University of Silesia , Bankowa 9, 40-007 Katowice , Poland
3 , Faculty of Biology and Environmental Protection, University of Silesia , Bankowa 9, 40-007 Katowice , Poland
Paper presents the phenomenon of thanatosis or death-feigning in selected aphids species. This specific reaction was predominantly analysed on the example of aphid subfamily Lachninae. Individuals of this group were used in experiments, during which a thanatotic response was induced with various results. The response differed from prolonged thanatosis, lasting for several minutes (Eulachnus rileyi), through shrinking behaviour (e. g. in Stomaphis graffii) to non-responsive species such as Cinara (Schizolachnus) pineti. The large interspecies variation of observed responses can be linked to other defensive mechanisms existing in the studied species, as well as to their mutualistic relationship with ants. The behaviour of shrinking is hypothesized to be the mutualistic response, developed from thanatosis, and being adapted to transportation by ant workers.
Thanatosis; immobility; adaptation; fitness; predation
Introduction
Thanatosis, or the so called Bdeath feigning^ or Bplaying possum^ is a
wellrecognized phenomenon in many animal taxa
(Honma et al. 2006)
. It is considered
as a basic mechanism of the Blast chance^ defence behaviour, where endangered
individual exhibits immobility and catatonic muscle tension. In this state the animal
does not lose its conscience and is aware of the phenomena taking place in the
environment
(Rogers and Simpson 2014)
. This behaviour, sometimes accompanied
by excreting various body fluids, is known both, in vertebrates as well as
invertebrates
(Miyatake et al. 2004)
. In case of insects, it is well known in stick-insects or
some groups of beetles, where immobility is very common defensive behaviour
(Godden 1972, 1974; Prohammer and Wade 1981; Gaiger and Vanin 2006;
Miyatake et al. 2008; Farkas 2016)
.
Apart from various defensive adaptations, aphids are known to exhibit
thanatosis, as a form of defence behaviour. It was observed as often exhibited
behaviour after fall off the host plant
(Losey and Denno 1998; Gish and Inbar
2006; Hodge et al. 2011)
by non myrmecophilous aphids. In case of
Acyrthosiphon pisum the aphids are known to maintain in thanatosis after the
drop off for various periods of time, dependent on the nature of the stimulus
(Wohlers 1981)
and after that they undertake movement of various characters
(Niku 1976)
. The time spent in thanatosis also depends on the height of fall
(Niku
1975)
. This behaviour was also observed in other species such as: Aualcorthum
circumflexum, Lipaphis erysimi, Macrosiphum euphorbiae and Megoura viciae
(Robert 1987)
, all these species being non myrmecophilous species feeding
predominantly on herbaceous plants. However, little is known about the aphid’s
thanatosis itself. More important seemed to be the behaviours of waving of
abdomens and/or legs, escape and searching of new host plant after drop off as
adaptive mechanisms against predators and other environmental factors
(Roitberg
et al. 1979; Mann et al. 1995; Hodge et al. 2011)
.
It may be suspected, that in case of apterous morphs of aphids (and contrary to alate
morphs), thanatosis could be promoted defensive behaviour in terms of natural
selection
(Ohno and Miyatake 2007)
. However, the adaptive nature of this phenomenon is
not well understood. Aphids due to their sedentary life mode exhibit a very wide range
of defensive mechanisms: waxy excreta, covering the body; alarm pheromones
inducing escape behaviour in the colony; mutualistic relationship with ants – which serve as
guards protecting aphid colony and even soldier morphs (Dixon 1998). In this view, it
seemed interesting to check, whether thanatotic behaviour is somehow correlated with
existing defensive mechanisms of aphids.
For this purpose several representatives of the aphid subfamily Lachninae were
assigned. This is a relatively homogenous group of aphids in respect of morphology,
connected with woody gymnosperms and angiosperms, showing a high variety of
ecological adaptations
(Jousselin et al. 2013; Chen et al. 2016)
. We chose this group
due to a single field observation of individual of obligate myrmecophilous, tree-trunk
feeding species Stomaphis graffii, which exhibited remarkable behaviour: after being
turned on back and touched with tweezers, it stopped moving and curled appendages
towards the body for a (...truncated)