Ecologistas encontram sinais sexuais nos olhos dos peixes.

published: Functional Ecology, 03 November 2010 (Wiley-Blackwell)

Two male sticklebacks in breeding condition,

with differing expression of their carotenoid

 (nuptial colouration).

How integument colour reflects its carotenoid content: a stickleback’s perspective

Thomas W. Pike

Bjørn Bjerkeng

Jonathan D. Blount

Jan Lindstrom

Neil B. Metcalfe

Carotenoid pigments are the source of many of the animal kingdom's most vivid colours; flamingos' pink feathers come from eating carotenoid-containing shrimps and algae, and carotenoid colours can be seen among garden birds in blackbirds' orange beaks and blue tits' yellow breast feathers.

These pigments play a crucial role in sexual signals. According to the study's lead author Dr Tom Pike of the University of Exeter: "Females typically use carotenoid colours to assess the quality of a potential mate, with more colourful males generally being regarded as the most attractive."

This long-held assumption is, however, hard to study because we see colour very differently to fish and previous studies have not taken such differences into account, instead comparing only the colours perceived by humans.

"The major difference between stickleback vision and our own is that they can see ultraviolet light, which is invisible to humans. This may be important because carotenoids reflect ultraviolet light as well as the red, oranges and yellows that we can see," Dr Pike explains.

The model developed by Dr Pike and colleagues from the University of Glasgow and Nofima Marine in Norway mimics the stickleback's visual system, allowing the researchers to determine what 'colours' the fish see. "The model tells us how much of the light reflected from a carotenoid signal is actually detected by a female and how this information might be processed by her brain, and so gives us exciting new insights into how females may use colour to choose the best mates," says Dr Pike.

Male sticklebacks can fine tune the colours they display to females by varying both the overall amount of carotenoids and the relative amount of the two constituent carotenoids, the red-coloured astaxanthin and the yellow tunaxanthin. The model reveals that sticklebacks' visual system and coloration are extremely well co-adapted, and that females are surprisingly good at assessing the quantity of carotenoids a male is able to put in his signal – which previous studies by the authors have shown is linked to his parenting ability.

The results will help ecologists get a better understanding of why carotenoid-based signals evolved in the first place, and provides insights into why males use the specific carotenoids they do. According to Dr Pike: "There are many carotenoids in the sticklebacks' diet, but males use only two of them for signalling; because the visual system evolved long before male coloration in this species, it suggests that males 'chose' to use those two carotenoids to make the most of what the female fish sees."

Full manuscript: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2010.01781.x/pdf

Qual truque os "glass catfish" utilizam para terem o corpo transparente?

Published: Dr Heok Hee Ng 

Issue of Practical Fishkeeping Magazine

Esta é uma pergunta para a qual não há resposta satisfatória, pois estamos apenas começando a entender a base física e anatômica de transparência em tecidos vivos.

Copyright © Neil Hepworth

Embora as bases físicas e anatômicas para alguns tecidos transparentes (ex.: a córnea e o cristalino do olho) são mais bem compreendidas do que outras, a situação no olho é única no sentido de que os tecidos são altamente modificados para a transparência e estas modificações (ex.: completa ausência de um sistema circulatório) não são aplicáveis ao tecido muscular.

Além disso, a maioria das principais modificações feitas para a transparência são ultra-estruturais e só podem ser vistas com o auxílio de um microscópio eletrônico. Para um tecido se tornar transparente, o mecanismo primário é reduzir a quantidade de luz dispersa quando a mesma passa pelo tecido: quanto menos luz disseminada pelo tecido, mais luz é emitida através dele e mais transparente o tecido.

Apesar de ainda não entendermos completamente como os tecidos, em especial o músculo, pode se tornar transparente, existem vários mecanismos que podem contribuir para explicar este fenômeno. O primeiro é que os peixes transparentes como o "glass catfish" (bagre fantasma ou bagre de vidro) têm corpos muito achatados. Essa forma achatada do corpo, diminui o potencial de disseminar luz (e, portanto, mais fácil será para tornar o tecido transparente).

Outro possível mecanismo é o envólucro ordenado de pequenas moléculas dentro do citoplasma das células para reduzir a dispersão da luz. Por fim, outras teorias defendem que os vários componentes subcelulares desses tecidos transparentes (ex.: mitocôndrias, ribossomos) devem ser pequenos e altamente dispersos.

Apesar de artigos de revisão recentes sobre este assunto, este campo tem mais perguntas do que respostas. São esperados estudos para se compreender melhor esse fenômeno.

Águas-vivas podem Influenciar na Instabilidade do Ecossistema

29 October 2010 - 16:13h

BBC News - Science and environment reporter 

by Mark Kinver

The causes behind jellyfish blooms are

difficult to disentangle, say the authors

Pesquisadores tentam identificar como as Águas-Vivas podem beneficiar os ecossistemas marinhos desestabilizados pelas alterações climáticas e sobrepesca. 

(Researchers have been trying to identify how jellyfish may benefit from marine ecosystems destabilised by climate change and overfishing.)

There is concern that a rise in jellyfish numbers could prevent depleted commercially important fish stocks recovering to historical levels.

However, a study by European scientists says more data is needed to understand what is happening beneath the waves.

Researchers from the UK and Ireland said samples collected from the Irish Sea since 1970 have recorded an increase in material from cnidarians (the division of the animal kingdom that includes jellyfish and coral), "with a period of frequent outbreaks between 1982 and 1991".

"There does appear to have been an increase in abundance since 1994 for the Irish Sea," said co-author Christopher Lynam, a researcher at the Centre for Environment Fisheries and Aquaculture Science (Cefas).

The team added that previous studies had recorded changes to marine ecosystems as a result of various factors, such as the removal of top predators, and changes to the distribution and characteristics of plankton.

Vast blooms of certain jellyfish
can cause havoc in affected areas

Jellyfish joyrid

These changes have led to a growing concern that the oceans may become increasingly dominated by jellyfish because "many gelatinous zooplankton species are able to increase in abundance rapidly and adapt to new conditions".

In 2007, an invasion of mauve stingers (Pelagia noctiluca) wiped out Northern Ireland's only salmon farm, killing more than 100,000 fish.In recent years, there have been a number of examples of sudden blooms of jellyfish in European waters - including the Irish, Mediterranean and Black seas - which have killed fish and closed beaches.

However, Dr Lynam was keen to point out that the team's study was dominated by the common moon jellyfish (Aurelia aurita), which was not responsible for wiping out the salmon.

The main concern, the team wrote, was the establishment of a "never-ending jellyfish joyride" in which the creatures become so established that it makes it almost impossible for commercial fish stocks to return to historical levels.

But Dr Lynam told BBC News: "I don't think that the hypothesis that jellyfish will come into an area and dominate, not allowing anything to come back again, is really supported.

"Such a nightmare scenario does not seem to be the case, when you consider the data and studies that have been carried out."

Complicated picture

He explained that the team looked at whether factors such as changes to the climate and overfishing were responsible for the increase in jellyfish abundance.

"It is quite a complicated set of possible linkages that need to be drawn, which we really only have a vague insight at the moment.

"For the recent period where we have good data, it appears as if sea surface temperature is the most important variable.

"This does not necessarily prove it of course, but it does appear to be benefiting jellyfish."

The team, using data provided by the UK Met Office, commented: "The regional seas of the northeast Atlantic have been warming for the past 15 years at a rate not experienced in recent centuries."

Overfishing has also been linked to the rise of jellyfish populations. Research suggests that commercial fishing during the 20th Century had resulted in a change in the Irish Sea's ecosystem.

The researchers wrote: "The overexploitation of herring during the late 1970s was followed by a period of ecosystem instability in the 1980s in which the frequency of occurrence of cnidarian material... rose to high levels, indicating outbreaks of jellyfish."

Dr Lynam added: "If you take out a lot of the plankton feeders, there could be more food for jellyfish so they might become more abundant. There may be feedback mechanisms that we are not aware of, so there does need to be further study."

But he cited examples in the North Sea and Black Sea where fish species had declined, leading to an increase in jellyfish abundance, but the introduction of measures such as limits on catches had resulted in a recovery of fish stocks.

The team urged for the monitoring of jellyfish to continue, and concluded: "The move to ecosystem-based fisheries management requires extensive ecological knowledge and an understanding of the risks posed by any indirect effects... of our utilisation of the sea's resources."