Castes in Social Insects Module Chemical Ecology, Ayasse Outline Castes in Social Insects 1. definition 2. castes in social insects 3. caste determination A. psychophysiological caste determination B. blastogenic und trophogenic caste determination - effect of juvenile hormone C. genetic caste determination 4. advantages of castes 5. summary 1
castes: individuals of a colony of one species that differ in morphology, physiology and behaviour. (ecological caused polymorphisms) (Wilson 1971) caste polymorphism: individuals with a functionally different form (e.g. workers and queen). further differentiation in (Wilson, 1985): physical castes: different function and morphology, same genotype (termites, ants). temporal castes: (=age polyethism) age dependent division of labour (honeybees, wasps) caste differentiation: different specification of the characteristics of individuals with identical genetic information caste determination: causes and mechanisms of caste differentiation (preimaginal or imaginal). caste regulation: caste determination in adult instars intercastes: morphological intermediates of two clearly distinguishable extreme forms 2
further differentiation mainly in ants: gynomorph: winged females or wingless females after mating (queenlike) ergatomorph: animal of a typical worker s form intermorph: commonly intermediates in ants all of the three forms can functionally be a queen (mated and fertile) or a worker larvae nymphs workers (higher termites: wingless, rudimentary genital apparatus, eyes reduced or absent) Isoptera Termitidae, Nasutitermes higher rermites 3
larvae nymphs workers (higher termites: wingless, rudimentary genital apparatus, eyes reduced or absent) workers of lower termites: immature stages, the worker function is being filled by nymphs and pseudergates pseudergates regressed from a.) nymphal stages by reduction of wing buds or b.) larvae by non-differentiating molts Isoptera Isoptera soldier with morph. features specialized for defence different types within the caste of soldiers: Mandibulate soldiers, Snapping soldiers, Nasute soldiers 4
Isoptera primary reproductives (colony founder) replacement reproductives (sec. developed) Hymenoptera queens workers different size, morphology and function in bees and wasps no subcastes division of labour is mostly based on temporal polyethism only ants with morphological subcastes 5
Hymenoptera Halictidae Hymenoptera Wasps 6
Age polyethism Hymenoptera Stingless bees and honeybees Hymenoptera Ants 7
Hymenoptera Ants Social insects Characteristics of Isoptera (termites) hemimetabol larvae contribute to caste system (lower termites) bisexual colony, castes consist of males and females XX XY mechanism of sex determination long-living males Hymenoptera (bees, ants, wasps) holometabol castes consist of adult animals only castes consist of females only haploid-diploid-mechanism of sex determination short-living males 8
1. definition 2. castes in social insects 3. caste determination A. psychophysiological caste determination B. blastogenic und trophogenic caste determination - effect of juvenile hormone C. genetic caste determination 4. advantages of castes 5. summary Epigenetic 1. Psychophysiological caste determination (often acting on adult individuals) pheromones and behaviour sexual predisposition (importance of mating) temporal predisposition (attractiveness and rank) 9
e.g. lower termites (Kalotermes) pheromones e.g. higher termites (Termitidae) Complex caste system and determination in a higher termite. What determines caste? Depending on species: Condition of colony (stress factors) Contact between nestmates Hormones, especially JH Pheromones, especially from reproductives from Gullen & Cranston 2000 10
Fire ants pheromones Polistes behaviour temporal predisposition: commonly the oldest female is fertile with developed ovaries 11
Sweat bees sexual predisposition: mated female becomes a queen 1. definition 2. castes in social insects 3. caste determination A. psychophysiological caste determination B. blastogenic und trophogenic caste determination - effect of juvenile hormone C. genetic caste determination 4. advantages of castes 5. summary 12
Epigenetic 2. Blastogenic and trophogenic caste determination nutrition factors in larval development (e.g. honeybee, royal jelly) egg ingredients (reserve substances, RNA content) colony size (important in determination of young queens) further: nest temperature during breeding in bumblebees nutrition factors in larval development castes similar size 13
in bumblebees nutrition factors in larval development castes similar size castes different size in honeybees nutrition factors in larval development (trophogenic determination) 14
in stingless bees nutrition factors in larval development in ants nutrition amount: larva fed with a high quantity of food develop into queens egg size: queens often hatch from large, yolk-rich eggs pheromones: reproductive queens can inhibit production of new queens colony size: important for the determination of young queens 15
in ants nest temperature during breeding: in species that overwinter its brood in the larval stage females develop into queens in winter and into workers in summer age of the queen: younger queens produce a lot of workers, old queens more reproductives Influence of juvenile hormone? on caste determination in ants 16
Influence of juvenile hormone on caste determination in honeybees JH mediator between environmental impacts (nutrition, pheromones, and morphological specification) 1. definition 2. castes in social insects 3. caste determination A. psychophysiological caste determination B. blastogenic und trophogenic caste determination - effect of juvenile hormone C. genetic caste determination 4. advantages of castes 5. summary 17
3. Genetic caste determination contribution of genetic factors to caste determination is poorly understood indications in: A. Higher termites certain castes consist of the same sex Genetic caste determination in higher termites JH application causes development of soldiers of the false sex epigenetic mechanisms 18
3. Genetic caste determination contribution of genetic factors to caste determination is poorly understood indications in: A. Higher termites certain castes consist of the same sex B. Bees Meliponinae queens develop from diploid eggs with paired heterozygous loci that determine the caste Genetic caste determination in Meliponinae two-locus model JH appl. causes development of queens nutrition factors Geraniol (Jarau et al. 2010) 19
3. Genetic caste determination contribution of genetic factors to caste determination is poorly understood indications in: A. Higher termites certain castes consist of the same sex B. Bees Meliponinae queens develop from diploid eggs with paired heterozygous loci that determine the caste C. Ants Genetic caste determination in Harpagoxenus Crossing experiments carriers of allele E are more frequently workers, of allele e more frequently queens E suppresses wing building Only ee can develop into queens ee, ee and EE develop into workers under presence of a nutrition factor epigenetic nutrition factor!!! 20
Advantages of castes division of labour and cooperative nest defence specialisation (tasks can be performed more effectively and at the same time) less mistakes because of the specialisation - Summary description of castes caste determination regulation of reproduction (morph./phys./behav.) (larval) (adult) bees minimal morph. food quantity physical (primitive eusocial) phys. + dominance pheromone behaviour mating, age bees morphological food quantity physical (highly eusocial) phys. +quality + dominance pheromone behaviour wasps minimal morph. food quantity physical (primitive eusocial) phys. + dominance pheromone behaviour age wasps morph. food quantity physical (highly eusocial) phys. (+ quality?) + dominance pheromone behaviour ants morph. food quantity physical (highly eusocial) phys. (quality) + dominance pheromone behaviour temp., egg factors lower termites morph. food (highly eusocial) phys. pheromones dominance pheromone behaviour further abiot. factors higher termites morph. food (highly eusocial) phys. pheromones dominance pheromone behaviour further abiot. factors 21