announcements mating and reproduction
TRANSCRIPT
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Announcements
• Reminder: office hours Monday 1-2,Tuesday 9:30-10:30
• Collection station to be made in lab.• Reading for today’s class:Rank, N. E., K. Yturralde and E.P. Dahlhoff.
2006. Role of contests in the scramblecompetition mating system of a leaf beetle.Journal of Insect Behavior, 19:699-716.
Mating and Reproduction• How sexes find each other• Courtship• Nuptial gifts• Sexual Selection
Sexual selection– Occurs when a trait that is costlyfor survival, but
– confers greater mating success– My explain sexual dimorphism
• Males larger than females- rare in insects• Exaggerated traits in males
Types of sexual selection• Intrasexual selection
– Contest competition– Scramble competition– Sperm competition
• Intersexual selection– Male has exaggerated trait– Females choose males depending on traitvalue
– Sex roles reversed if males performmore parental care than females
Contest competition• Frequent fights over territory or access to
females• Males monopolize females• Often exaggerated traits in males• Positive assortative mating (large males
mate with large females) probablybecause large females lay more eggs
Large male wins Exaggerated structure
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Scramble competition• Scramble to be first to mate• Little monopolization of females• No consistent body size effect
– small may be better for maneuverability– large may have advantages if it relates
to speed
Mixed strategy within dung beetles
• Contest- Largedhorned malesmonopolize tunnelsin which femaleslive
• Scramble- Smallhorned males sneakaround large malesor dig a side tunnel
Copulation and sexual selection• Copulation often prolonged in
insects– Female may try to break off
sooner if male is less desirable– Male may try to prolong
copulation to maximizefertilization
• Male accessory gland secretionmay– Repress female receptivity to
mating by others– Stimulate female oviposition
Sperm competition• What really counts
– Male: number ofoffspringfathered
– Female: highestquality mates
• Intersexual conflictmay occur overwhich sperm fertilizeeggs
Sperm competition• Last-in-first out systems
– Spermatophore closestto oviduct mostsuccessful
– Males push previoussperm higher intospermatheca
• Sperm removal– Scoop out previoussperm
– Flush out previoussperm
Outcomes of sexual selection
– Rapid evolution of genitalia
– High variation within and amongspecies, more than needed forcopulation
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• Can prevent interspecies mating• Can also result from intersexual conflict
over control of sperm
Variation in female reproductive tract Morphological evolution in males
• Females of all three species look alike• Rapid evolution of male structures
associated with mating
Results of sexual selection– Further exaggeration of traituntil balance between cost andbenefit established
– May result in new species
Chrysomela aeneicollis
• Little sexual dimorphism,females larger thanmales
• Little evidence of strongsexual selection
• males frequently fight formates
• mating behavior is easyto study in the laboratory
Study Questions
• How does mating behavior in the fieldrelate to behavior in the laboratory?– with male competition– under female choice
• How does size affect mating successin males and females?
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Field component
Laboratory Component
• field observations
• collect:
– mating pairs
– unmated males
• male competition trials
• female choice trials
• morphologicalmeasurements
MF
M
Morphological measurements• measured
– elytra length– femur length– thorax width
• compare size withmating success
femur
Male fights in the field
• males locked mandibles and bit each othersfront appendages
• interactions lasted 2 to 88 minutes• One male paired with female after 35% of
fights. Sometimes intruder, sometimesresident.
• females usually left fighting males (32 of 37)interactions
Most common behaviors in the field
Snapshot 2008-04-02 06-29-36
Large females mate with large males in the field
Female elytra length (mm)
Mal
e el
ytra
leng
th (m
m)
Mating males weren’t larger thansingle males
Mated males Unmated malesmean mean
Elytra length 4.52 4.59 P > 0.2
Femur length 1.29 1.29 P > 0.7
Thorax width 2.32 2.34 P > 0.6
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Design of laboratory tests• half of field mating males were paired with
their field partner• other half of field mating males were paired
with new females
1 1
20 20
21 22
39 21
Female choice trial
Behaviors observed in thelaboratory
Behavior Competition Trial Choice Trialsitting 43% 64%feeding 8% 11%walking 21% 21%mating 14% 2%mate-guard 9% 1%fighting 7% 0%
Field female New female
Male competition trials
Mated male Unmated male
Prop
ortio
n of
tim
e m
atin
g
Female mate choice trials
Field female New female
Prop
ortio
n of
tim
e m
atin
g
Mated male Unmated male
Prop
ortio
n of
tim
e m
atin
g
Female elytra length (mm)
Female size and female mating success
0
0.1
0.2
0.3
0.4
0.5
0.6
5 5.1 5.2 5.3 5.4 5.5 5.6 5.7
°°
°
°
°
°
°
°
°°
° °°
°°°
5.8
new female field female
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Conclusions of beetle study
• Mostly likely a scramble mating system• Males do not monopolize females• Large males do not mate more than smaller ones
• Fighting and competition do occur• Females prefer ‘better’ competitors• Males prefer large or ‘new’ females