10/7/2011. What is a male and what is a female? Both males and females are selected to maximize their success in reproduction.

Transcription

1 Insect Reproduction Insect Reproduction Major Objectives 1. Name the two agents of sexual selection. 2. Describe, with examples, the four major benefits of being choosy. 3. Explain why males are often the competing sex and females are the choosy sex. 4. Become capable of figuring out the mating system of a new species to science. 5. Explain the ecological circumstances that lead to sex role reversal in insects. What is a male and what is a female? Both males and females are selected to maximize their success in reproduction 1

2 What limits reproductive success? Female reproductive success h h /i / hi i i i Natural Selection & Sexual Selection Male reproductive success Gail L. Patricelli Sexual selection can be extremely strong! Intra- versus inter- Sexual Selection Male-male competitions Gail L. Patricelli Mate choice Hence I am led to suppose that the females generally prefer, or are most excited by the more brilliant males". Charles Darwin 2

3 PROTECTION NEST SITES Indirect benefits GOOD GENES A Mormon cricket female (Requena verticalis) eats her spermatophore meal Hanging flies,hylobittacus apicalis Thornhill 1976, 1980, 1984 the nuptial gift Gwynne, D.T Katydids and Bush-crickets: Reproductive Behavior and Evolution of the Tettigoniidae. Cornell University Press, Ithaca New York PROTECTION Copyright 2004 Tim Nichols Golden Dung Flies Mating - Scathophaga stercoraria - Mineral County, West Virginia, USA October 26,

4 PROTECTION OVIPOSITION SITES PROTECTION OVIPOSITION SITES Indirect benefits GOOD GENES Which male has better genes? Who should she choose? How should she choose?? Golden Brown Shield Bug, Anchises parvulus Family Pentatomidae Male choice do males care? Male choice do males care? *When parents contribute equally to offspring they should be equally choosy* But, even when fathers contribute less, they still may be somewhat choosy. If female quality varies a lot If males invest more than DNA in offspring (e.g. nutritious spermatophore) (Trivers 1972, Bonduriansky 2001) 4

5 Intra- versus inter- Sexual Selection Male weapons Stalk-eyes Dsc.discovery.com Male-male competitions Mate choice Male weapons Horns Antlered flies Male weapons Antlers Elk Horned beetles in a single genus, Onthophagus Male mating systems Female defense polygyny 1. Female defense polygyny 2. Resource defense polygyny 3. Lek defense polygyny 4. Scramble defense polygyny Emlen & Oring 1977 Science 5

6 Female defense polygyny Resource defense polygyny Some wasps in the family Eumenidae build a series of brood cells in the same place. Newly-emerged males guard a group of cells from which females may emerge. Also harlequin beetles AND the pseudoscorpions (Coleoptera: that Cerambycidae) ride them Acrocinus longimanus Competitions are a Coleopteran version of jujitsu Lek defense polygyny Stalk-eyed flies Cotton, S., Small, J., Hashim, R., & Pomiankowski, A. (2010) Eyespan reflects reproductive quality in wild stalk-eyed flies. Evolutionary Ecology. 24, Zeh et al 1992 Biotropica Scramble defense polygyny e.g. Mayflies What predicts the mating system? 1. Female defense polygyny 2. Resource defense polygyny 3. Lek defense polygyny 4. Scramble defense polygyny Emlen & Oring 1977 Science 6

7 What is the mating system for the lovebug? The Lovebug!! Other mating behaviors The Lovebug!! Plecia nearctica (DIPTERA: BIBIONIDAE) Thornhill 1980 (Assignment #2 reading) Plecia nearctica (DIPTERA: BIBIONIDAE) Mate guarding (this is not the same as female defense polygyny) Helps ensure paternity of offspring Copulation = fertilization The Lovebug!! Plecia nearctica (DIPTERA: BIBIONIDAE) One sperm from Drosphila bifurca. Image by Romano Dallai Copulatory courtship Copulatory courtship is likely a way males attempt to persuade females to use their sperm A bizarre way of mating Includes tapping, stroking, or rubbing with antennae, legs, or genitalia William Eberhard 1991, 1994, 1996 More info: 7

8 A bizarre way of mating Parental investment How do insects invest in their offspring? More info: Alex Trillo Parental investment How do insects invest in their offspring? Parental investment How do insects invest in their offspring? Egg size (amount of yolk) Careful placement of eggs Egg (and juvenile) protection Male parental care Why is male parental care rare in insects? Males generally have higher fitness by leaving and looking for other mates Certainty of PATERNITY is often low Giant Water Bug Family (Belostomatidae) 8

9 What leads to monogamy in males? 1. Female or resource defense is not feasible 2. Offspring are not likely to survive without help from the dad 3. Female forces monogamy on the male by eating him Male behavior ensures paternity! Male parental care Giant Water Bug Family (Belostomatidae) Giant water bug males Males invest morein parental care than females Male fecundity is more limited than female (only so many can fit on back!) Males are more choosy than females Females compete over access to males! Other role reversed taxa Sea horses, pipefish, sea spiders, and jacanas Insect Reproduction Have a great weekend! Major Objectives 1. Name the two agents of sexual selection. 2. Describe, with examples, the four major benefits of being choosy. 3. Explain why males are often the competing sex and females are the choosy sex. 4. Become capable of figuring out the mating system of a new species to science. 5. Explain the ecological circumstances that lead to sex role reversal in insects. 9