Karl Popper believed there was a distinction between scientific and non-scientific theories. He defined a scientific theory as one that “makes a risky prediction”. This is achievable when an event possible of refuting that theory can be imagined. He believed theories capable of forbidding something from happening were the strongest due to the obvious refutability possible if that something does in fact occur. Finally, to produce any evidence in support of a theory, attempts must be made to falsify through genuine testing (experiments). The three words he uses to sum up his criteria for a scientific theory are falsifiablility, refuatbility, and testability. In other words, proof of a theory can only be defined by a lack of evidence supporting an alternative hypothesis obtained during experiments attempting to refute the theory in question.
In the Mathews paper, the authors wanted to test two hypotheses about mate-guarding
in male snapping shrimp. They hypothesized males should be able to distinguishing
the sexual receptivity of another female snapping shrimp and males should prefer
to guard and associate with sexually receptive females over less sexually receptive
females. Figure 2 illustrates their test of the first hypothesis through the
prediction that males would spend more time in water with chemical cues from
sexually receptive females than in untreated water or water with cues from males
and less sexually receptive females. The figure depicts the amount of time males
spent in water with chemical cues from various other shrimp (Intermolt female/male,
molted female/male, and premolt female/male) minus the time males spent in untreated
(control) water. If males spend more time in water with cues from sexually receptive
(premolt) females than with water with other cues or no treatment, their prediction
is supported. However, if the males spend more time in any of the other water
treatments this hypothesis must be rejected.
The figure illustrates the males’ ability to determine chemicals produced
by sexually receptive females. As shown, males spent more time in water infused
with chemicals from premolt females than time in untreated water. In replicates
of this experiment using water from different males and females, no positive
response to the stimulus water was greater than with premolt females if existant
at all. This figure also demonstrates a preference by males to spend time in
untreated water instead of the other stimulus waters, especially intermolt males
and females. All of these findings support the original hypothesis because if
the reverse was found (which was possible), they would refute the original hypothesis.
Therefore, these findings supporting their hypothesis would be accepted by Popper
as scientific based on their falsifiability and collection from a genuine test.
There are several qualities a scientific theory must have in order for it to receive the approval of Karl Popper. All predictions must be risky, meaning that there is some amount of uncertainty associated with them. Science is prohibitive, so strong theories should forbid certain events from happening; the more they forbid the stronger they are. Experiments or studies should be designed to disprove theories because falsification is more telling than confirmation. Nothing can ever be completely proven; there are only many instances of supporting evidence and a failure to disprove. To Popper, there can be a thousand confirmations of a theory, but if there is not a case imagined where this theory could be wrong, the confirmations are not significant and the theory is not valid.
In “Tests of the mate-guarding hypothesis for social monogamy,”
Mathews was experimenting with the mate-guarding behaviors of A. angulatus because
of the socially monogamous qualities they possess. She hypothesized that males
that are able to predict molting cycles and chose to guard females that are
more receptive would be more successful at copulation. Her predictions were
that 1) males must be capable of assessing female receptivity through some physical
signals and 2) males will pair with and guard females that are more receptive
as they will bring more reproductive success. These predictions explicitly state
what Mathews hopes to find, while at the same time implicitly state that if
these things do not happen, her hypothesis is incorrect. If the male A. angulatus
are unable to distinguish between receptive and unreceptive females, Mathews’
hypothesis will be disproven. She will also be disproven if the males do not
choose females that are more receptive. Like Einstein with relativity, Mathews
presented a hypothesis and set out to disprove it. Fortunately for her, the
experiments give supporting evidence of her hypothesis, showing in Figure 2
that males spent more time on average in waters treated with premolt females.
This means that males would chose premolt females significantly more often than
molted or intermolt females. While this evidence supports the hypothesis, it
does not prove it, nor can it ever be proven. This theory and experiment would,
I think, gain the approval of Popper for its risky nature and refutability.
The study performed by Lim et al. (2004) focused on how the variable expression of a single gene may explain the difference in mating behavior between monogamous prairie voles and polygamous meadow voles. Lim et al. certainly approached this study from a proximate perspective. Previous studies with a wide variety of organisms had shown that high levels of a particular vasopressin receptor (V1aR) located in the ventral forebrain are associated with monogamous behavior. In addition, it had been discovered that this vasopressin receptor is present in larger quantities in prairie voles than in meadow voles. Therefore, the authors hypothesized that over expressing the V1aR gene in the ventral forebrains of polygamous meadow voles would result in more monogamous behavior.
This study was centered on proximate causation because it examined a mechanism
that was responsible for an immediate change in social behavior. The scientists
looked at the behavior on a molecular genetic level and found that the proximate
factor accounting for the difference in mating behavior was varying amounts
of a receptor that binds to one hormone. This mechanism affected the behavior
being studied in the organisms’ lifetimes and there were no inferences
made about the past or future of the behavior.
If the primary interest of this study were ultimate causation, the authors would
have investigated the influence of evolutionary forces on the mating behavior
of the two vole species over time. Furthermore, they would have been interested
in why monogamy may be beneficial to prairie voles while polygamy may suit meadow
voles. There were no predictions that prairie voles being monogamous or meadow
voles being polygamous provided any increase in fitness to either species in
their respective environments. Above all, the authors were seeking to answer
a “how” question rather than a “why” question.
Possible ultimate hypotheses for the monogamy exhibited by prairie voles and
the polygamy displayed by meadow voles would be based on the environmental conditions
of each species and the evolutionary history of the behavior. For example, male
prairie voles choose one mate to avoid intense sperm competition because the
sex ratio of the population is heavily favored towards males. Therefore, being
monogamous increases the likelihood that male prairie voles will reproduce.
However, meadow voles are polygamous because the females in the population have
unusually low fecundity. For this reason, male meadow voles have evolved to
mate with as many females as possible to ensure that their genetic material
is passed on.
The paper that I decided to look at for this question is the prairie vole paper
by Lim et. al. In this paper they look at the differences between monogamous
prairie and pine voles (Microtus montanus) and promiscuous meadow or montane
voles (microtus montanus). In particular they observe differences in V1aR receptors
in the ventral pallidum. Monogomous prairie and pine voles have microsatellite
regions in the 5’ regulatory region, differing from the promiscuous voles
who do not have this. They wanted to look at how overexpression of these receptors
influence pair bonding behaviors. Because this paper looks at how genetic differences
and neural mechanisms involving dopamine and vasopressin receptors, it is dealing
with proximate mechanisms. The idea was that changes induced in the neural mechanisms
in promiscuous voles could lead to pair bond formations. These changes were
induced by overexpressing the V1aR gene by AAV-mediated gene transfer in the
promiscuous species, and comparing to controls. This paper directly looks at
what allows a behavior to occur, and the mechanisms that are behind it, and
they found that a simple manipulation of one gene can have huge impacts on pair
bonding behavior, a proximate mechanism
If the behavior was looked at from the ultimate mechanisms, it would focus on the advantages that have evolved over time and what has a greater fitness value. A hypothesis for this would be that pair-bonded prairie voles have higher fitness in areas that have limited resources. Selection for increased V1aR expression, resulting in pair bonds would help solve this problem because two parents could help care for their young. A female that has a male bonded for life would have help with providing resources to their young and giving them proper materials they need for survival. Promiscuous species would be less likely to survive because the female would likely have no help, and offspring may struggle to survive.
When analyzing the paper, “Enhanced Partner Preference in a Promiscuous Species by Manipulating the Expression of a Single Gene,” by Lim et al., 2004, it is clear that the authors were addressing a proximate hypothesis of animal behavior. The study answers the “how” questions associated with the differences between prairie vole and meadow vole social behavior at the molecular and genetic levels. In the study, the authors looked to see if enhancing expression of the vasopressin V1a receptor (V1aR) in meadow voles would lead to an increase in partner preference formation. The reasoning behind this study was that the V1aR is expressed to a much greater degree in the brains of monogamous voles when compared with promiscuous voles. The authors then presented the hypothesis that differences in V1aR expression within vole brain tissue resulted in different social behavior. Thus the prediction was that enhancing V1aR expression in meadow vole brains would result in increased partner preference formation and altered social behavior that was similar to that of prairie voles. As a result, the paper is clearly addressing a proximate question.
Although the paper directly addresses a proximate hypothesis, it is possible,
and useful, to expand the findings of this paper to question an ultimate hypothesis.
It is unlikely that the difference observed between prairie voles and meadow
voles is arbitrary, and thus there must be a “why” hypothesis that
addresses this directly. The differences in genetic expression and social behavior
likely evolved from an external pressure that differs between the two habitats
of the voles. Given that prairie voles are monogamous, i.e. they prefer to mate
with a single individual and remain with said individual, it appears likely
that prairie voles do not frequently encounter potential mates in the wild.
On the other hand, the promiscuous nature of meadow voles indicates that they
may be opportunistic in their mating habits, and frequently come into contact
with potential mates. These differences in exposure to potential mates could
be a result of increased predation and decreased resources in areas inhabited
by prairie voles. Additionally, it is known that male prairie voles have home-ranges
that are roughly the size of female home-ranges, and thus males do not pass
through many female home-ranges throughout their lives. On the other hand, male
meadow vole home-ranges can be up to ten times the size of a female home-range,
and thus the male meadow voles frequently travel through the home-ranges of
multiple females. Therefore, one could propose an ultimate hypothesis for the
differences in vole mating by stating that monogamy in prairie vole social behavior
evolved as a way to ensure the potential for lifelong breeding in a species
that does not frequently encounter potential mates due to increased predation,
decreased resources, and a small male home-range when compared to the promiscuous
meadow vole.
A study by Carazo, et al. (2004) examined the ability of male beetles to discern the reproductive status of female beetles in order to choose a mate. The researchers wanted to know if reproductive status effected male mate choice, and if so, whether chemical cues were a factor in this choice. The experiment showed a significant preference for courting and mating with mature females over immature females, and virgin females over mated females. When testing filter paper exposed to female chemical cues, it was found that the males showed the same preference in odor as they did for mating choice in the previous experiment, showing that chemical cues are sufficient in giving a male enough information to choose a female mate.
This paper shows a test of a proximate hypothesis to explain the mating choices
of a male beetle. Proximate hypotheses ask questions involving how a behavior
occurs and what biological mechanisms cause it to happen. This paper specifically
looks into how beetles choose their mates (maturity and mating experience),
as well as the physiological mechanism behind this choice (olfactory cues).
This paper does not test ultimate hypotheses, which look into why a behavior
takes place and what adaptive value it confers upon the individual.
Ultimate hypotheses in this case would attempt to explain why males choose mature
females over immature ones. One possible explanation is the higher fecundity
of mature females. This would put a selective pressure on males to choose mature
females, since it would provide them with a higher number of offspring. The
ultimate explanation for male preference for virgins may also involve an increased
likelihood to reproduce. In beetles, sperm competition occurs, where multiple
males inseminate one female. Thus, it is possible that mating with a non-virgin
female will put the male’s sperm in competition with others, and therefore
lower the likelihood of one of its own offspring being born. Thus, there would
be a selective pressure for a male to prefer virgin females.
The German word “umwelt” can be translated into English as “around the world”. In the fields of ethology and behavioral ecology this term is used to describe how an animal perceives the world around it. Perception of surroundings is highly variable among animals of different species. For example, two animals of different species could be occupying the same environment while perceiving this environment in completely different ways. This is because animals of different species have different filtering systems that are specific to their individual needs. An animal’s filtering system filters out stimuli that are not important to the animal’s fitness.
The concept of nerve cell thresholds explains the mechanisms by which an animal
perceives a stimulus and why some stimuli elicit a behavioral response while
others do not. For this reason, this concept is closely related to the idea
of the umwelt and filtering systems. When an animal encounters a stimulus, electrical
signals are passed from neuron to neuron relaying a message to the brain, which
will initiate a response. In order for these signals to be passed along, the
stimulus must be strong enough to surpass the nerve cell’s threshold.
This means that the inside of the membrane must be depolarized enough to fire
an action potential. If a stimulus is not important enough, the nerve cell threshold
will not be reached, an action potential will not be fired, and no message will
be sent to the brain.
The sound experiment performed with the moths can be explained both in terms
of the umwelt/filtering system and the concept of nerve cell thresholds. The
figure displaying the results of the experiment shows that, at some sound frequencies,
the volume needs to be very high in order for the moths to detect anything.
However, at other frequencies the moths were able to detect the sound even if
it was very faint. It is probable that these easily detectable frequencies are
important to the moths’ fitness. Perhaps a common predator of this species
of moth emits sounds at these frequencies. It is also possible that other moths
emit sounds at these frequencies as a means to attract a mate. The filtering
system of the moths filters out sounds at other frequencies unless they are
extraordinarily loud.
The frequencies detected by the moths at low volume were strong enough stimuli
to surpass the nerve cell threshold. This caused the nerve cell to fire, send
the signal to the brain, and bring about an observable response. The frequencies
detected by the moths only at high volume would not have been strong enough
stimuli to surpass the nerve cell threshold if they were presented at lower
volume. If all frequencies had been presented to the moths at equally low volumes,
these frequencies would not have brought about a response because the nerve
cell threshold would not have been reached. Again, this indicates that the moth
is more sensitive to certain sound frequencies because they are somehow relevant
to survival and reproduction.
Umwelt is the way an organism perceives the world around it. Organisms Umwelts differ because they have different filtering mechanisms that determine what stimuli they detect and respond to. One part of an organism’s filtering mechanisms may be neurons that detect touch, sounds, or other external stimuli. If the stimuli is above a certain threshold important to the organism, the neuron will “fire,” sending a signal down the neuron, across synapses, and to innervate an effector that takes action. If a stimuli is not above the nerve cell threshold, the neuron does not fire, and the organism does not notice or respond to this stimuli. The given figure shows the sound intensity (volume/power) at which the moth species can detect a range of sound frequencies. This figure represents the moth’s filtering system for sound frequencies. These moth’s nerve cell thresholds are lowest for sounds at a frequency of 5-6 kHz. That means that the strength of the stimulus (intensity) needed to cause a neuron and organism response is least at 5-6 kHz. Additionally, the moths have a low nerve cell threshold for sounds with frequencies from about 40-90kHz. Although the strength of the stimulus need for the neurons to fire is much higher than that needed to detect sound at 5-6kHz, it is still lower than the intensity needed to “fire” neurons at other frequencies.
If we think about the moth’s Umwelt as a result of its sound filtering
systems, we can see that the moth perceives the “sound world” by
its sensitivity to two ranges of frequencies. One of these ranges is specific
and the moth is very sensitive to these specific frequencies at 5-6 kHz. This
indicates that there is some stimuli that is extremely important to the moth’s
fitness. Perhaps this is the frequency at which a reproductively mature moth
may emit sounds to find a mate. Mates that cannot hear this sound at the low
intensity that it is emitted will not be able to find a mate and thus will not
pass on their genetic material to the next generation. This ensures the continuation
of moth genes that allow moths to have this low nerve cell threshold for sounds
at 5-6 kHz. Detection of the sounds from 40-90KHz appear to be important, but
not as pertinent as detection of sounds at 5-6 kHz because the threshold is
higher for these sounds. This frequency could be the frequency of sonar used
by bats to detect moth prey. While this filtering system is important for a
bats fitness, it is not as crucial as the filtering system needed to find a
mate. In other words, it is great for the moth if it can avoid being eaten,
but this does not matter if that moth cannot find a mate, because these predator-avoidance
mechanisms cannot be passed down to the moth’s offspring, because this
moth will not have offspring. Therefore, we can see an organism’s umwelt
as shaped and defined by the factors and stimuli that contribute to their fitness
and propagation of genetic material. Thus, the differences in the way organisms
perceive the world are dependent on differences in factors affecting reproductive
success and organism fitness.
The increase in testosterone during the mating season might increase male sparrow’s
desire to mate. This might result in an increase in courting and mating behaviors
as well as territory preparation. To test this hypothesis with an observational
study (1) I would observe male sparrows throughout the year and create time
budgets, paying close attention to mating/courting and territory preparation
behaviors. Plotting the frequency that these specific behaviors occur over the
whole year would produce a figure showing when these behaviors are most common.
I would expect to see these behaviors at the highest frequency during the same
time as the testosterone increase shown in Figure 3, with a decrease in frequency
when testosterone levels are low. Plotting the testosterone levels of a specific
time of year with the frequency of mating/courting behaviors at that same time
on a scatter plot would help determine if any significant correlation exists
between the two.
To perform a manipulative study (2), I would take male sparrows in the lab during a time of year when testosterone levels are low. I would artificially increase testosterone level through injections and then observe their behaviors, giving them access to females and territory building supplies. Behavioral observations before the increase in testosterone would also be required. Obviously, care would be taken to keep conditions stable throughout the trials, providing access to females and supplies to pre-trial, post-increase, and control males. After analyzing the frequency of mating/courting behaviors both before and after the increase in testosterone would show if the hormone had any effect on the behaviors. Taking measures of the level of testosterone in the blood would help create a figure plotting exact levels of testosterone against frequency of the behavior. Using different levels of testosterone on different birds would also show a possible threshold for how much testosterone is needed before the behaviors are actually triggered.
In conjunction, these two studies along with Figure 3 could show that increases
in testosterone, both naturally and artificially, are capable of inducing mating/courting
behaviors. This would support my hypothesis that testosterone triggers these
behaviors if the frequency of mating behaviors increased at the same time testosterone
naturally increases (figure 3) and when testosterone levels were artificially
increased. If these studies produced different results, such as no increase
in behavior when testosterone was artificially increased, then it may suggest
a different trigger for the start of these behaviors.