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Effects of UV-A and Predation Threat on Mantle Pigmentation of Freshwater Snails (Radix balthica)

Yang, Xi (2012) BIOM35 20121
Degree Projects in Biology
Abstract
Abstract
We studied the effects of UV-A radiation and predatory fish on mantle pigmentation of freshwater snails Radix balthica. The results showed that UV radiation and fish chemical cue induce larger ratios of pigmented area on mantle, respectively and when combined. UV radiation and predatory fish chemical cue seem to affect mantle pigmentation independently. The ratios (0~100%) of pigmented mantle area in the different treatments were: 0.41 ± 0.17 (Control), 0.52 ± 0.19 (Fish), 0.67 ± 0.16 (UV), 0.72 ± 0.12 (UV + Fish), respectively. We suggest that the darker phenotypes are adaptations to UV radiation and predation pressure, however the mechanisms of the formation of those two adaptations might be completely different. According to... (More)
Abstract
We studied the effects of UV-A radiation and predatory fish on mantle pigmentation of freshwater snails Radix balthica. The results showed that UV radiation and fish chemical cue induce larger ratios of pigmented area on mantle, respectively and when combined. UV radiation and predatory fish chemical cue seem to affect mantle pigmentation independently. The ratios (0~100%) of pigmented mantle area in the different treatments were: 0.41 ± 0.17 (Control), 0.52 ± 0.19 (Fish), 0.67 ± 0.16 (UV), 0.72 ± 0.12 (UV + Fish), respectively. We suggest that the darker phenotypes are adaptations to UV radiation and predation pressure, however the mechanisms of the formation of those two adaptations might be completely different. According to our results, UV radiation is a stronger selective factor of mantle pigmentation compared to predation pressure. It’s however unclear how UV and predation pressure affects each other in the inducement of mantle pigments.

Popular science summary:

Put on a cape against the Sun, and the hungry fish.
An interesting experiment to test how ultraviolet (UV) radiation and predation pressure affect on mantle pigmentation of freshwater snails (Radix balthica).

Ultraviolet (UV) radiation from sun ray is the culprit of sunburns. In order to protect themselves from the Sun, many animals and plants produce UV-blocking dark pigments and transport them to the body surface in order to form UV-shield. Pigments also help animals to form camouflage colouration, which protects them from visual hunters. This is very important for slow animals like snails since they usually can’t run away from fast hunters like fish. It was noticed that snail R. balthica has various types of dark patterns on their back (mantle pigmentation), under their see-through shells. The size and shape of “dark capes” vary between individuals. You may ask why do they have the “dark capes”, is it some kind of camouflage? Or could it be some kind of sunburn-shield? If you think further, another interesting question could be: why do they have different “dark capes” within the same species? With the same questions we conducted this experiment, and expected to see UV and predation pressure could make some differences on the “dark capes”.

After settled many newly hatched snails down in the aquariums, we installed UV lamp up on the ceiling to simulate the UV from the Sun. As for predation pressure, we added the water collected from snail-eating-fish aquarium, since it contains the alarming chemicals cue which makes snails stay alert. When exposed to the chemical cue, snails usually “run” to hide under the shelters or leave the water surface due to the “horror of fish”. After 8 weeks, the snails exposed to UV and/or “horror of fish” got larger “dark capes” on their backs, compared to the ones who lived in a calm and peaceful environment (no-UV or no-fish). We suggest that the stimulation from UV boosts up the production of pigments. The pigments were transferred to the body surface, thus a UV-shield was formed, just like men got tanned in sunbed. Predation pressure makes snails form up larger “dark capes” too, which could be a way of camouflage. It was also manifested by mantle pigmentation.

Our results suggested that practitioners need to be more careful when using mantle pigmentation in species identification, since individuals can develop into rather different appearances due to different environment they live in. Although we got known that it is environmental factors which lead the variances of mantle pigmentation, more questions were raised up and needed to be answered, such as: what is the mechanism behind the formation of camouflage, and what kind of camouflage was that? But anyway, this is a good start!


Advisors: Johan Ahlgren, Christer Brönmark
Master´s Degree Project 30 credits in Aquatic Ecology, 2012
Department of Biology, Lund University (Less)
Please use this url to cite or link to this publication:
author
Yang, Xi
supervisor
organization
course
BIOM35 20121
year
type
H2 - Master's Degree (Two Years)
subject
keywords
phenotypic plasticity, mantle pigmentation, UV radiation, predator chemical cue
language
English
id
3616005
date added to LUP
2013-03-22 09:34:16
date last changed
2013-03-22 09:34:16
@misc{3616005,
  abstract     = {Abstract
We studied the effects of UV-A radiation and predatory fish on mantle pigmentation of freshwater snails Radix balthica. The results showed that UV radiation and fish chemical cue induce larger ratios of pigmented area on mantle, respectively and when combined. UV radiation and predatory fish chemical cue seem to affect mantle pigmentation independently. The ratios (0~100%) of pigmented mantle area in the different treatments were: 0.41 ± 0.17 (Control), 0.52 ± 0.19 (Fish), 0.67 ± 0.16 (UV), 0.72 ± 0.12 (UV + Fish), respectively. We suggest that the darker phenotypes are adaptations to UV radiation and predation pressure, however the mechanisms of the formation of those two adaptations might be completely different. According to our results, UV radiation is a stronger selective factor of mantle pigmentation compared to predation pressure. It’s however unclear how UV and predation pressure affects each other in the inducement of mantle pigments.

Popular science summary:

Put on a cape against the Sun, and the hungry fish.
An interesting experiment to test how ultraviolet (UV) radiation and predation pressure affect on mantle pigmentation of freshwater snails (Radix balthica).

Ultraviolet (UV) radiation from sun ray is the culprit of sunburns. In order to protect themselves from the Sun, many animals and plants produce UV-blocking dark pigments and transport them to the body surface in order to form UV-shield. Pigments also help animals to form camouflage colouration, which protects them from visual hunters. This is very important for slow animals like snails since they usually can’t run away from fast hunters like fish. It was noticed that snail R. balthica has various types of dark patterns on their back (mantle pigmentation), under their see-through shells. The size and shape of “dark capes” vary between individuals. You may ask why do they have the “dark capes”, is it some kind of camouflage? Or could it be some kind of sunburn-shield? If you think further, another interesting question could be: why do they have different “dark capes” within the same species? With the same questions we conducted this experiment, and expected to see UV and predation pressure could make some differences on the “dark capes”.

After settled many newly hatched snails down in the aquariums, we installed UV lamp up on the ceiling to simulate the UV from the Sun. As for predation pressure, we added the water collected from snail-eating-fish aquarium, since it contains the alarming chemicals cue which makes snails stay alert. When exposed to the chemical cue, snails usually “run” to hide under the shelters or leave the water surface due to the “horror of fish”. After 8 weeks, the snails exposed to UV and/or “horror of fish” got larger “dark capes” on their backs, compared to the ones who lived in a calm and peaceful environment (no-UV or no-fish). We suggest that the stimulation from UV boosts up the production of pigments. The pigments were transferred to the body surface, thus a UV-shield was formed, just like men got tanned in sunbed. Predation pressure makes snails form up larger “dark capes” too, which could be a way of camouflage. It was also manifested by mantle pigmentation. 

Our results suggested that practitioners need to be more careful when using mantle pigmentation in species identification, since individuals can develop into rather different appearances due to different environment they live in. Although we got known that it is environmental factors which lead the variances of mantle pigmentation, more questions were raised up and needed to be answered, such as: what is the mechanism behind the formation of camouflage, and what kind of camouflage was that? But anyway, this is a good start!


Advisors: Johan Ahlgren, Christer Brönmark
Master´s Degree Project 30 credits in Aquatic Ecology, 2012
Department of Biology, Lund University},
  author       = {Yang, Xi},
  keyword      = {phenotypic plasticity,mantle pigmentation,UV radiation,predator chemical cue},
  language     = {eng},
  note         = {Student Paper},
  title        = {Effects of UV-A and Predation Threat on Mantle Pigmentation of Freshwater Snails (Radix balthica)},
  year         = {2012},
}