3/2/17 Reproduction Courtship & Mating in Insects • How do the sexes find each other? – Light – Swarming (male only/ female only) – Leks (male aggregations) • Defend territory against males • Court arriving females – Pheromones What do they do once they Types of Courtship find each other? Courtship • Visual displays • Close range intersexual behavior that induces sexual receptivity before and during mating. • Allows mate choice among and within species. 1 3/2/17 Types of Courtship Types of Courtship • Visual displays • Visual displays • Ritualized movements – ‘Dancing’ induces • Ritualized copulation in receptive movements females. – Often VERY stereotyped • Tactile stimulation and species-specific. • Sound production • Tactile stimulation Ritualized courtship in Nasonia parasitic wasps Types of Courtship Nuptial Gifts • Visual displays • 3 forms • Ritualized – Cannibalization of movements males • Tactile stimulation – Glandular product • Sound production – Nuptial gift • Nuptial gifts • Prey • Salt, nutrients 2 3/2/17 Evolution of nuptial feeding Sexual Cannibalization • Female advantages – Nutritional benefit • Rather extreme – Mate choice (mate with good provider) • Male actually does not • Male advantages willingly give himself – Helping provision/produce his offspring up… – Female receives sperm while feeding rather than – Where would its mating with someone else potential reproductive • Male costs benefit be? – Capturing food costs energy and incurs predation • Do females have risk increased – Prey can be stolen and used by another male. reproductive success? Glandular gifts Nuptial gifts • Often part of the spermatophore (sperm transfer unit) – Occupy female while sperm is being transferred – Parental investment by male • Generally a food item (usually prey) • Also regurgitations (some flies) • But beware the Cubic Zirconia, ladies 3 3/2/17 Sexual selection Types of sexual selection • Intrasexual selection – Contest competition – Scramble competition – Sperm competition • Intersexual selection • Occurs when a trait evolves that is costly for survival, but… – Male has exaggerated trait • Confers greater mating success – Females choose males depending on trait value • May explain sexual dimorphism – Sex roles reversed if males perform more parental – Males larger than females: rare in insects care than females – Exaggerated traits in males Contest competition Scramble competition • Frequent fights over • Scramble to be first to mate territory or access to • Little monopolization of females females • Males monopolize • No consistent body size effect females – Small size may be better for • Often exaggerated maneuverability traits in male – Large size may have advantages if it relates to speed 4 3/2/17 Mixed strategy Copulation and sexual with dung beetles selection • Contest: larged- • Copulation often horned males prolonged in insects – Female may try to break monopolize tunnels off sooner if male is less in which females live desirable – Male may try to prolong • Scramble: Small- copulation to maximize horned males sneak fertilization • Male accessory gland around large males secretion may… or dig a side tunnel. – Repress female receptivity to mating by others – Stimulate female oviposition Sperm competition Sperm competition • What really counts • Last-in-first-out systems – Spermatophore closest – Male: number of to oviduct most offspring fathered successful – Female: highest – Males push previous sperm higher into quality mates spermatheca – Intersexual conflict • Sperm removal may occur over – Scoop out previous which sperm fertilize sperm eggs – Flush out previous sperm. 5 3/2/17 Dragonflies Sexual Conflict of Interest • Particularly common in promiscuous mating systems • Absent in monogamous mating systems. Why? • Taken to extremes in males with genitalic armature 6 3/2/17 Sexual Conflict of Interest Sexual Conflict of Interest • Particularly common in promiscuous • Particularly common mating systems in promiscuous • Absent in mating systems monogamous • Absent in mating systems. monogamous Why? mating systems. • Taken to extremes Why? in males with • Taken to extremes genitalic armature in males with genitalic armature Outcomes of sexual selection Variation in female reproductive tract • Can prevent interspecies mating • Rapid evolution of genitalia • Can also result from intersexual conflict over • High variation within and among species, control of sperm more than needed for copulation 7 3/2/17 Morphological evolution in males Results of sexual selection • Morphological evolution in males often much more rapid than in females • Further exaggeration of trait until balance – Especially characters related to secondary sexual traits between cost and benefit established – Females of different species often morphologically • May result in new species. indistinguishable. e.g. Rheumatobates water striders What’s the result of all of What’s the result of all of these shenanigans? these shenanigans? • Reproduction! • Egg-laying • Successful fertilization accomplished through will result in fertilized ovipositor egg and egg-laying: – Formed from abdominal oviparity. appendages (plesiomorphic), or – Formed from posterior segments (substitutional) 8 3/2/17 Ovipositor Insect Reproduction • Variously modified • Means of producing to insert eggs into offspring appropriate – Oviparity: egg-laying substrate. initiates egg development. – Ovoviviparity – Viviparity Insect Reproduction Insect Reproduction • Means of producing • Means of producing offspring offspring – Oviparity – Oviparity – Ovoviviparity – Ovoviviparity – Viviparity • Allows offspring to • Pseudoplacental – Egg/larvae nourished take advantage of in reproductive tract highly ephemeral • Hemocoelous resource – Larvae free in hemocoel – Viviparity • Adenotrophic – Milk glands, larva pupates immediately on deposition. 9 3/2/17 OR DISPENSE WITH THE SHENANIGANS Types of parthenogenesis • Parthenogenesis • Production of females from unfertilized eggs: • Females produce Thelytokous parthenogenesis viable unfertilized – Can occur via automixis: meiosis occurs, two eggs products of meiosis refuse to form diploid female. – Can occur via apomixis: no meiosis, diploid egg is • Found in nearly all produced via mitosis. insect orders • Production of males from unfertilized eggs: Arrhenotokous parthenogensis – Always produced via automixis Parthenogenesis in Hymenoptera Types of parthenogenesis and Thysanoptera (and some others) • Haplodiploidy • Obligatory • Females (queen & workers) • Facultative produced from fertilized eggs or (occasionally) from – Seasonal in aphids automictic thelytokous – Asexual reproduction parthenogenesis: diploid during summer • Male drones always – Sexual reproduction produced from unfertilized in spring and fall eggs through arrhenotokous parthenogensis: haploid. 10 3/2/17 Hermaphroditism • What is it? • Exceedingly rare in insects (given that every other bizarre genetic system exists). • Only one genus of scale insect: Icerya 11 .