My aim here is to record some ideas about social behaviour in insects that indication an early step evolution might have taken to arrive at the levels of adaptation seen among the termites and hymenopteran societies. Parental care appears to be an essential prerequisite for the evolution of eusociality. However, Martin Nowak and co-authors in an extraordinary paper, show that evolution of parental care can be a small step, so some of the larvae I consider here, though there is no clear evidence of parental care, may be poised on the brink of the evolution of advanced insect societies ( Nowak, et al 2010).
I start with a interesting but little known proto-termite studied by Vicky Taylor (Taylor 1981). The animal concerned is the larva of the beetle Ptinella which, like a termite, consumes dead wood in which it lives. The result is the reduction of the habitat over time and the production of a winged dispersal form, the alate. The parallel to termite society is striking. Ptinella is not alone as a pre-social insect. Another is the larva of the rain pool dwelling chironomid midge, Chironomus imicola. Just as in Ptinella, C. imicola inhabits a ephemeral habitat which diminishes in size after rain due to evaporation. Larvae respond to the resulting crowding with the production of a giant carnivorous larva. The emerging giant adult is adapted to long distance dispersal (McLachlan and Ladle 2001).
.jpg)
Fig 1. An aggregation of beetle larvae on a leaf (From Costa, J. T. 2007).
A fine example of aggregation in the larvae of insects is shown in Fig.1., and more can be found in Collins Nature Guides (Gibbons 1999). The topic is explored by James Costa (Costa 2006), drawing on a wide assemblage of examples from among the arthropods. Returning to the chironomid midge, the larvae of most species inhabit the mud of more permanent inland waters. These larvae typically build tubes of mud and silk which lie horizontally on the mud surface (McLachlan and Ladle 2009). The tubes are strikingly even in their distribution.
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Fig. 2. The distribution of tubes of the midge Chironomus sp at high population densities in the laboratory. From (McLachlan 1983).
Indeed, larvae will not build closer than a body length to neighbours, late arrivals appear to be physically expelled. Low density treatments in laboratory rearing trials yield poor survival rates. So, there is a hint of some sort of density dependent social interaction necessary for successful development. In this connection, the enhancement of the innate immune response under crowded conditions is relevant (Ruiz-Gonzalez, Moret et al. 2009).
In some small ponds, larval tubes are built vertically from the mud surface rather than horizontally. This may be a response to the ecology of such pools where temperatures are high and oxygen levels low. Dissolved oxygen levels are probably highest at the water surface in contact with the air. If this is so, drawing water into tubes from near the water surface would be adaptively appropriate. An hypothesis that it is oxygen that determines tube shape is a testable hypothesis but to prevent a tube from falling over, cooperation is required from neighbours. This could be seen as a step toward sociality (Krebs and Davies 1981) p120. Cooperation between neighbours necessary for support is shown by larvae of Microtendipes chorlis? The end result is a massive communal construction.
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Fig. 3. A mass of mutually supporting larval tubes of Mircotendipes chlois?, take for the bottom of a small peat pool in Scotland. The structure is somewhat collapsed due to removal from the water. The picture is c. 15 cm across.
The same kind of cooperative tube construction is shown also by the larvae of the rain pool dwelling chironomid Polypedilum vanderpalnki (Hinton 1968). In both P. vanderplanki and M. chlois? larval densities are high making possible the construction of mutually supporting vertical tubes.Thus temporary waters such as rain pools and small peat pools may have nurtured the origin of life on earth e.g. (Weisz 1959) p53 Fig 3.11, and may have aslo to the evolution of eusociality.
references
Costa, J. T. (2006). The other insect societies. London, Belknap Press.
Gibbons, R. (1999). Insects of Britain & Europe. Collins Nature Guides. London, HarperCollins Publishers Ltd.
Hinton, H. E. (1968). "Reversible suspension of metabolism and the origin of life. ." Proceedings of the Royal Society, London (B). 171, 43-47.
Krebs, J. R. and N. B. Davies (1981). An Introduction to Behavioural Ecology. London, Blackwell Scientific Publications.
McLachlan, A. J. (1983). "Life-history tactics of rain-pool dwellers." Journal of Animal Ecology. 52, 545-561.
McLachlan, A. J. and R. Ladle (2001). "Life in the puddle: behavioural and life-cycle adaptations in the Diptera of tropical rain pools." Biological Reviews, 76, 377-388.
McLachlan, A. J. and R. Ladle (2009). "The evolutionary ecology of detritus feeding in the larvae of freshwater Diptera." Biological Reviews. 84, 133-141.
Ruiz-Gonzalez, M. X., Y. Moret, et al. (2009). "Rapid induction of immune density-dependent propoholaxis in adult social insects." Biological Letters doi:10.1098/rsbl.
Taylor, V. A. (1981). The adaptive and evolutionary significance of wing polymorphism and parthenogenesis in Ptinella Motschulsly (Coleoptera: Ptillidae). Ecological Entomology. 6, 89-98.
Weisz, P. B. (1959). The Science of Biology. New York, McGraw-Hill.
.jpg)
Fig 1. An aggregation of beetle larvae on a leaf (From Costa, J. T. 2007).
A fine example of aggregation in the larvae of insects is shown in Fig.1., and more can be found in Collins Nature Guides (Gibbons 1999). The topic is explored by James Costa (Costa 2006), drawing on a wide assemblage of examples from among the arthropods. Returning to the chironomid midge, the larvae of most species inhabit the mud of more permanent inland waters. These larvae typically build tubes of mud and silk which lie horizontally on the mud surface (McLachlan and Ladle 2009). The tubes are strikingly even in their distribution.
.png)
Fig. 2. The distribution of tubes of the midge Chironomus sp at high population densities in the laboratory. From (McLachlan 1983).
Indeed, larvae will not build closer than a body length to neighbours, late arrivals appear to be physically expelled. Low density treatments in laboratory rearing trials yield poor survival rates. So, there is a hint of some sort of density dependent social interaction necessary for successful development. In this connection, the enhancement of the innate immune response under crowded conditions is relevant (Ruiz-Gonzalez, Moret et al. 2009).
In some small ponds, larval tubes are built vertically from the mud surface rather than horizontally. This may be a response to the ecology of such pools where temperatures are high and oxygen levels low. Dissolved oxygen levels are probably highest at the water surface in contact with the air. If this is so, drawing water into tubes from near the water surface would be adaptively appropriate. An hypothesis that it is oxygen that determines tube shape is a testable hypothesis but to prevent a tube from falling over, cooperation is required from neighbours. This could be seen as a step toward sociality (Krebs and Davies 1981) p120. Cooperation between neighbours necessary for support is shown by larvae of Microtendipes chorlis? The end result is a massive communal construction.
.png)
Fig. 3. A mass of mutually supporting larval tubes of Mircotendipes chlois?, take for the bottom of a small peat pool in Scotland. The structure is somewhat collapsed due to removal from the water. The picture is c. 15 cm across.
The same kind of cooperative tube construction is shown also by the larvae of the rain pool dwelling chironomid Polypedilum vanderpalnki (Hinton 1968). In both P. vanderplanki and M. chlois? larval densities are high making possible the construction of mutually supporting vertical tubes.Thus temporary waters such as rain pools and small peat pools may have nurtured the origin of life on earth e.g. (Weisz 1959) p53 Fig 3.11, and may have aslo to the evolution of eusociality.
references
Costa, J. T. (2006). The other insect societies. London, Belknap Press.
Gibbons, R. (1999). Insects of Britain & Europe. Collins Nature Guides. London, HarperCollins Publishers Ltd.
Hinton, H. E. (1968). "Reversible suspension of metabolism and the origin of life. ." Proceedings of the Royal Society, London (B). 171, 43-47.
Krebs, J. R. and N. B. Davies (1981). An Introduction to Behavioural Ecology. London, Blackwell Scientific Publications.
McLachlan, A. J. (1983). "Life-history tactics of rain-pool dwellers." Journal of Animal Ecology. 52, 545-561.
McLachlan, A. J. and R. Ladle (2001). "Life in the puddle: behavioural and life-cycle adaptations in the Diptera of tropical rain pools." Biological Reviews, 76, 377-388.
McLachlan, A. J. and R. Ladle (2009). "The evolutionary ecology of detritus feeding in the larvae of freshwater Diptera." Biological Reviews. 84, 133-141.
Nowak, M. A., Tarnita, C. E. and Wilson, E. O. (2010). The evolution of eusociality. Nature. 466, 1057-1062.
Ruiz-Gonzalez, M. X., Y. Moret, et al. (2009). "Rapid induction of immune density-dependent propoholaxis in adult social insects." Biological Letters doi:10.1098/rsbl.
Taylor, V. A. (1981). The adaptive and evolutionary significance of wing polymorphism and parthenogenesis in Ptinella Motschulsly (Coleoptera: Ptillidae). Ecological Entomology. 6, 89-98.
Weisz, P. B. (1959). The Science of Biology. New York, McGraw-Hill.
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