Effects of multiple mating in males on female reproduction: evidence for sperm depletion in Trinidadian guppies
(2025) BION03 20242Degree Projects in Biology
- Abstract
- According to sexual selection theory, males should benefit more from mating with multiple partners than females do as male investment into offspring production is typically lower. However, male reproductive success might not increase indefinitely with an increasing number of female mating partners. Male ejaculates are limited, and so mating with multiple females over a short period of time may cause a decrease in the quantity and quality of sperm, which might, in turn, affect female reproductive success. Here, we investigated the effect of multiple mating in males on female reproductive success in a laboratory population of Trinidadian guppies (Poecilia reticulata), a species known for its polygamous mating system. We created mating groups... (More)
- According to sexual selection theory, males should benefit more from mating with multiple partners than females do as male investment into offspring production is typically lower. However, male reproductive success might not increase indefinitely with an increasing number of female mating partners. Male ejaculates are limited, and so mating with multiple females over a short period of time may cause a decrease in the quantity and quality of sperm, which might, in turn, affect female reproductive success. Here, we investigated the effect of multiple mating in males on female reproductive success in a laboratory population of Trinidadian guppies (Poecilia reticulata), a species known for its polygamous mating system. We created mating groups of two different sizes: 16 males had weekly one-on-one mating opportunities with four females and 14 males with seven females, respectively. Females (n = 170) were immature virgins when first mated, and we recorded their age at first parturition, the number of offspring in the first litter, and their probability of reproductive failure until the age of 160 days. We found that a larger mating group size caused a 13% delay in female age at first parturition and a 32% increase in litter size. While the former is due to either sperm depletion or male mating fatigue, the latter is likely a consequence of the females’ larger size when giving birth at an older age. Only 5.3% of females did not reproduce, and so statistical power for detecting an effect of mating group size on the probability of reproductive failure was insufficient. Accordingly, even though twice as many females failed to reproduce in the larger mating groups (3.6% vs. 1.8%), this difference was not significant. Our findings suggest that, even in a highly polygamous species, male reproductive performance might be limited, potentially rendering the strength of sexual selection more similar between males and females than conventionally assumed. (Less)
- Popular Abstract
- Effects of multiple mating in males on female reproduction in Trinidadian guppies
In Trinidadian guppies (Poecilia reticulata), multiple mating is a common phenomenon, where both females and males’ mate with multiple partners. Males are known to benefit most from multiple matings, as multiple matings is equal to a higher number of offspring. However, multiple mating over a short period of time can also cause problems, as it can cause for a decrease in quality and quantity of the male’s sperm, a process called sperm depletion. As multiple mating affects sperm quality, this in turn affects the reproductive success of the females. In this study, we therefore investigate how the multiple mating of males affects the females age at first... (More) - Effects of multiple mating in males on female reproduction in Trinidadian guppies
In Trinidadian guppies (Poecilia reticulata), multiple mating is a common phenomenon, where both females and males’ mate with multiple partners. Males are known to benefit most from multiple matings, as multiple matings is equal to a higher number of offspring. However, multiple mating over a short period of time can also cause problems, as it can cause for a decrease in quality and quantity of the male’s sperm, a process called sperm depletion. As multiple mating affects sperm quality, this in turn affects the reproductive success of the females. In this study, we therefore investigate how the multiple mating of males affects the females age at first birth, the number of offspring she produces at her first birth, as well as the risk for female infertility. Infertility, which is when an individual is unable to produce any offspring, can occur due to sperm depletion, but can also occur through pair-infertility. In this, the male and female have a genetic mismatch that causes the female’s infertility.
In this experiment, we set 32 mating groups of two different sizes. 14 mating groups had 1 male and 7 females, 18 mating groups had 1 male and 4 females. For each female, we registered her age at first mating, which is the age she had in days when she was first introduced to a male, age at first parturition and the number of offspring in her first litter. For each fish, we measured their weight at age 120 days.
Within the mating groups, we were able to test for pair-infertility. When a female did not mate within the first 100 days of the mating process, she was excluded from the mating group and was remated at age 114 days with 2 new males. If she did not reproduce any offspring at age 160 days, she was stated infertile.
Results
We found that for the females in mating groups with 7 females, the age at first parturition was higher, meaning they were older when they had their first offspring. The difference for the mating groups of 7 females, compared to the groups with 4 females, was 13.4%.
For number of offspring, we found that in mating groups with 7 females, they produced bigger litters, meaning they had more offspring than the females who were in mating groups of 4 females. The average litter size in the big mating groups was 31.5% bigger.
We also found a correlation between age at first parturition and the number of offspring in litter 1. This means that for all females with a later age at first parturition, the number of offspring was higher. A reason for this is that when a female is bigger, she tends to produce more offspring. As female guppies continue to grow with age, the females with a later age at first parturition are also bigger at first parturition.
The fertility rates in this experiment were high, with a 100% fertility rate in males, and a 94.7% fertility rate in females. The rates of infertility were also similar between the two mating groups. Due to this, we are unable to provide any evidence of pair-infertility within this setup
Master’s degree Project in biology, with speciation in aquatic ecology, 60 credit, Department of Biology, Lund University
Supervisor: Anja Felmy, Department of Biology, Lund University (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9212891
- author
- van der Walle, Tess Makenna
- supervisor
-
- Anja Felmy LU
- Flavio Di Giorgio LU
- organization
- course
- BION03 20242
- year
- 2025
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9212891
- date added to LUP
- 2025-09-19 15:28:26
- date last changed
- 2025-09-19 15:28:26
@misc{9212891,
abstract = {{According to sexual selection theory, males should benefit more from mating with multiple partners than females do as male investment into offspring production is typically lower. However, male reproductive success might not increase indefinitely with an increasing number of female mating partners. Male ejaculates are limited, and so mating with multiple females over a short period of time may cause a decrease in the quantity and quality of sperm, which might, in turn, affect female reproductive success. Here, we investigated the effect of multiple mating in males on female reproductive success in a laboratory population of Trinidadian guppies (Poecilia reticulata), a species known for its polygamous mating system. We created mating groups of two different sizes: 16 males had weekly one-on-one mating opportunities with four females and 14 males with seven females, respectively. Females (n = 170) were immature virgins when first mated, and we recorded their age at first parturition, the number of offspring in the first litter, and their probability of reproductive failure until the age of 160 days. We found that a larger mating group size caused a 13% delay in female age at first parturition and a 32% increase in litter size. While the former is due to either sperm depletion or male mating fatigue, the latter is likely a consequence of the females’ larger size when giving birth at an older age. Only 5.3% of females did not reproduce, and so statistical power for detecting an effect of mating group size on the probability of reproductive failure was insufficient. Accordingly, even though twice as many females failed to reproduce in the larger mating groups (3.6% vs. 1.8%), this difference was not significant. Our findings suggest that, even in a highly polygamous species, male reproductive performance might be limited, potentially rendering the strength of sexual selection more similar between males and females than conventionally assumed.}},
author = {{van der Walle, Tess Makenna}},
language = {{eng}},
note = {{Student Paper}},
title = {{Effects of multiple mating in males on female reproduction: evidence for sperm depletion in Trinidadian guppies}},
year = {{2025}},
}