Recognition in burying beetles (Nicrophorus spp., Silphidae, Coleoptera) [Elektronische Ressource] / vorgelegt von Sonia Whitlow

Med1b322

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• Publié par: albert-ludwigs-universitat_freiburg
• Publié le: 01 janvier 2004
• Nombre de lectures: 9
• Langue: English

Extrait

Recognition in burying beetles
(Nicrophorus spp., Silphidae,
Coleoptera)







Inauguraldissertation
zur Erlangung der Doktorwürde
der Fakultät für Biologie
der Albert-Ludwigs-Universität
Freiburg in Breisgau







Vorgelegt von Sonia Whitlow




2003









Dekan der Fakultät für Biologie: Prof. Dr. H. Kleinig
Promotionsvorsitzender: Prof. Dr. K.F. Fischbach
Betreuer der Arbeit: Prof. Dr. K. Peschke, Prof. Dr. J.K. Müller
Referent: Prof. Dr. K. Peschke
Koreferent: Prof. Dr. J.K. Müller
3. Prüfer: Prof. Dr. S. Rossel

Tag der Verkündung des Prüfungsergebnisses: 5. Februar 2004 Contents
Contents Page number

1 Introduction 1
1.1 The insect cuticle 1
1.2 Case study: Nicrophorus species 3
1.3 Questions to be addressed 4

2 Materials and methods 6
2.1 Capture, care and breeding 6
2.2 Preparation and performance of behavioural experiments 6
2.2.1 Washing 6
2.2.2 Behavioural tests 7
2.3 Chemical analyses 8
2.3.1 Extraction 8
2.3.2 Silica gel chromatography 8
2.3.3 Solid-phase microextraction (SPME) 8
2.3.4 Dimethyl disulphide (DMDS) derivatisation 9
2.3.5 Gas chromatography and mass spectrometry (GC and
GC-MS) 9
2.3.6 Identification of chemicals 10
2.3.6.1 n-Alkanes 10
2.3.6.2 Olefins 11
2.3.6.3 Methyl-branched hydrocarbons 13
2.3.6.4 The position of the double bond 14
2.4 Statistical methods 15

3 Results 18
3.1 Types of chemicals 18
3.1.1 Hydrocarbons 18
3.1.2 n-Alkanes 18
3.1.3 Olefins 18
3.1.4 Monomethylalkanes 19
3.1.5 Dimethylalkanes 19
3.1.6 Trimethylalkanes 20
3.1.7 Other cuticular chemicals 20
3.2 Contamination of the cuticular extract 20
3.2.1 Haemolymph 20
3.2.2 Anal secretion 22
3.2.3 Substrate 22
3.3 Body parts 23
3.4 The pattern of cuticular chemicals 25
3.5 Chain length 25
3.6 The species-specific pattern of chemicals 27
3.6.1 N. vespilloides (E) 27
3.6.2 (C) 29
3.6.3 N. defodiens 29
3.6.4 N. vespillo 30
3.6.5 N. humator 30
3.6.6 N. fossor 31
3.6.7 N. sayi 31
3.6.8 N. orbicollis 31 Contents
3.6.9 N. tomentosus 31
3.6.10 Necrodes littoralis 31
3.6.11 Oiceoptoma thoracica 31
3.6.12 Ptomascopus morio 32
3.7 Species specificity of the cuticular chemicals 32
3.8 Principal Component Analysis (PCA) 39
3.8.1 N. vespilloides (E) 39
3.8.2 (C) 42
3.8.3 N. vespillo 43
3.8.4 N. humator 45
3.8.5 N. defodiens 47
3.9 The recognition system in N. vespilloides (E) 52
3.9.1 Response of females to mature conspecific females 52
3.9.2 Information in the cuticular chemicals used by females 52
3.9.3 The sex-specific pattern detected by females 54
3.9.4 Response of males to mature conspecific females 55
3.9.5 Information in the cuticular chemicals used by males 56
3.9.6 The sex-specific pattern detected by males 57
3.9.7 Response of females to immature conspecific individuals 60
3.9.8 Response of males to immature conspecific individuals 61
3.9.9 Response of N. vespilloides (E) males to other species 63
3.9.10 Response of (E) females to other species 64

4 Discussion 66
4.1 The insect cuticle 66
4.2 Types of hydrocarbons 67
4.2.1 n-Alkanes 67
4.2.2 Olefins 67
4.2.3 Monomethylalkanes 67
4.2.4 Dimethylalkanes 68
4.2.5 Trimethylalkanes 68
4.3 The prevention of desiccation 69
4.4 Species-specificity of the cuticular pattern 70
4.5 Sex-specificity 72
4.6 Age- 73
4.7 The recognition process in Nicrophorus species 73
4.7.1 The importance of cuticular chemicals in recognition 74
4.7.2 Determination of conspecifics by male N. vespilloides (E) 74
4.7.3 Determination of conspecifics by female (E) 75
4.7.4 Determination of immature conspecifics by female
N. vespilloides (E) 76
4.7.5 Determination of immature conspecifics by male
(E) 77
4.7.6 Interactions with different species 77

5 Conclusions 80

6 Bibliography 82

7 Acknowledgements 90
Contents
8 Appendix 91
Introduction - 1 -
1. Introduction
Burying beetles (Nicrophorus species) are unusual in that they have an extensive biparental brood
care system. This is rare in insects and such a complicated system can be found in very few species
e.g. the desert tenebrionid beetle, Parastizopus armaticeps (Rasa 1999). The method by which
males and females are able to distinguish each other as potential sexual partners may be the ability of
individuals to detect sex- and species- specific chemicals or patterns of chemicals on the cuticle.

1.1 The insect cuticle
The waxy (lipid) layer on the cuticles of insects plays a vital role in many aspects of insect life. These
lipids, which cover the surface of the cuticle, consist mainly of hydrocarbons, particularly n-alkanes,
methylalkanes and olefins. Small amounts of fatty acids, fatty acid esters and aldehydes are also
present (Jackson & Blomquist 1976).

The main purpose of the waxy layer is to help to prevent desiccation (Hadley 1984), a function
which has allowed insects to successfully colonise land. Individuals of the same species e.g. the
cockroach, Blatella germanica, are often found to vary the quantity and abundance of certain
hydrocarbons with habitat and season to reduce transpiration as much as possible (Young et al.
2000). Other uses include the prevention of the entry of micro-organisms, and the exploitation of
information as kairomonal cues, which parasites use to find their hosts (Review: Blomquist & Dillwith
1985). The complex nature of the lipids has also allowed insects to evolve a very effective
communication system. The cuticular pattern has been found to enable discrimination of species and
sexual partners, as well as the release of mating behaviour at close range, and nest mate recognition
in social insects, for example ants (Formicidae), honey bees (Apidae) and paper wasps (Vespidae)
(see Singer 1998 for a general review). Termites are another excellent example of social insects
which use cuticular components for recognition systems. The cuticular patterns of each species of
termite are unique (Haverty & Thorne 1989). If an individual of a different species enters a colony,
members of that colony eject the intruder from the nest. It was noted that the signature for this
recognition was present in the hydrocarbon fraction of the cuticular extract which allowed
discrimination of individual specificity (Bagnères et al. 1991).
Introduction - 2 -
The presence of a sex pheromone on females allows males to discriminate conspecific sexual
partners and releases copulatory behaviour. In the rove beetle, Aleochara curtula, two main sex
pheromones were identified, (Z)7-heneicosene and (Z)7-tricosene (Peschke & Metzler 1987). It
was found that immature males also produce the female sex pheromone, but the levels decreased
during the first two weeks after emergence (Peschke 1986). In the house fly, Musca domestica,
females are recognised mainly by the presence of (Z)9-tricosene (Dillwith et al. 1982).
Vitellogenesis stimulates changes in the cuticular hydrocarbon pattern and triggers production of the
sex pheromone (Carlson et al. 1971; Dillwith et al. 1982). The presence of methylalkanes further
increases the copulatory attempts of males (Nelson et al. 1981). Olefins were also found to release
copulatory behaviour in some Drosophila species (Oguma et al. 1992).

Chemicals which just appear on the cuticles of either males or females of a species allow for easy
discrimination. However, many species do not show any qualitative differences in the cuticular
patterns of mature males and females. For example, not all species in the Drosophila virilis group
had female-specific sex pheromones (Bartelt et al. 1986). In spite of this, males still release sexual
behaviour when they came into contact with females and this may be due to certain cuticular
hydrocarbon patterns on the females. This is also the case with alfalfa leaf cutter bees, Megachile
rotundata. It was found that females have higher concentrations of certain n-alkenes than males
(Paulmier et al. 1999). The absence of a unique sex pheromone still allows recognition of
conspecific females by the ability of males to determine differences in the proportions of chemicals on
individuals. In fact, it is possible that the insects may be r