CC BY
51
UDC 574.32:574.38
V P Perevozkin, V S. Galkin
ALTERNATIVE wAYS OF NUTRITION OF MALARIAL MOSQUITOES’ LARVAE (DIPTERA, CULICIDAE) AS IMPORTANT COMPONENTS OF THEIR ADAPTIVE COMPLEXES
Behavioral features of malarial mosquitos’ larvae Anopheles atroparvus (Diptera, Culicidae) are studied and connected with additional ways of meal reception - a substratum scraping and cannibalism. Results of experiments demonstrate that larvae of young and advanced stages Anopheles have various trophic and spatial niches in biotopes. Fall of food concurrence among stages and pressure of cannibalism on larvae of younger stages are reached. At the same time, individuals of advanced stages A. atroparvus actively dive on depth of ten centimeters in search of forage, being switched over to alternative type of a food - the scraping.
Key words: malarial mosquitoes, developmental stages, cannibalism, scraping, behavior, concurrence.
Introduction
It is known that malarial mosquitos’ larvae use several ways of food acquisition [1]. The basic type of food is the filtration of the particles afloat from the water surface. Additional forms of forage reception are the scraping from underwater substratum and cannibalism. Switching over to the basic type of food on the alternative one’s occurs at a lack of meal and high density of preimaginales developmental stages. Such feature of food acquisition expands ecological flexibility of mosquitos’ larvae and allows the limited number of individuals to pass to a pupa stage, and after an imago. It is obvious that probability of achievement of imago stage is higher among those larvae who used the widest spectrum of possible ways of food acquisition and who leave behind other individuals from the same generation in their development. In this case the difficult stage structure is formed in larval populations, and the cannibalism becomes one of the important regulatory factors of number of younger stage [2]. Thus group selection leads to fastening of behavioural adaptations and allow larvae to use more full available resources and to lower negative pressure of the concurence in populations.
The purpose of the present work was research of features of alternative ways of food acquisition (scraping, cannibalism) as important components of adaptive complexes of malarial mosquitos’ larvae Anopheles atroparvus (Diptera, Culicidae).
Materials and methods
Larvae of 1-st and 4-th stage from a laboratory line of malarial mosquitoes Anopheles atroparvus were used in experiences.
In the first experiment, on cannibalism, the one-liter jar was used and tap water in volume of 500 ml was poured in it. 50 larvae of 1-st and 4-th stage simultaneously were located by the instrumentality of a medical pear in a vessel with water. During experiment larvae were not fed. Further once a day number of individuals of two stages was counted up.
In the second experiment in which ability to a food from a substratum of 4-th stage larvae was become
clear, the 3-liter jar was used by certain height of liquid column in which 50 individuals Anopheles was placed. Two series of experiences were made: at the first series quantity of scrapings from a bottom by larvae was started to note in 10 min after their carrying over to the vessel; at the second - in 35 min. Those individuals were taken into account only, who dived and tried to extract a forage from the bottom of the vessel. The initial height of the tap water column was specified at 6 cm level. Water was added on 2 cm higher in each subsequent case then the previous level, up to 18 sm. In all cases calculation of submersion was carried out through 10 min after addition of water within 10 min.
Results and discussion
The cannibalism shows the most at Anopheles larvae of advanced stages in point of individuals of young stages [2]. As a rule, the hierarchy of larvae of different development stages is formed in water bodies. Individuals of 4-th stage occupy a leading position in this hierarchy. Their interaction with young larvae is reflected in number dynamics of young larvae and on genetic structure of population in whole in the overpopulated biotopes [3]. This process was conditionally named by “stage selection”. This form of selection should inevitably lead to forming of a complex of behavioural and physiological adaptations of young stages larvae, which reduce probability of death from congeners-can-nibals (who doesn’t pursue the victims actively).
Effects of cannibalism in the experiment were considered by giving an example of interaction of 1-st and 4-th stage larvae Anopheles atroparvus.
Calculation of larvae in a vessel every other day of experiment showed that 24 individuals of the first stage survived only from 50 one’s; it makes 48 % of the initial quantity of individuals. Their quantity was reduced to 7 one’s (14 %) next day, and there aren’t individuals of the first stage in a vessel for the third day (Fig. 1).
It is necessary to notice that the death of 4-th stage larvae isn’t registered in experiment. At the same time, remains of 1-st stage larvae aren’t discovered in a ves-
Days
Fig. 1. Speed of death of larvae of 1-st stage Anopheles atroparvus from cannibalism of 4-th stage larvae. n - quantity of 1-st stage larvae
sel. Thus, results of experience are evidence that the cannibalism was a unique cause of death of 1-st stage larvae in experiment.
Most probably, in the first place individuals of 1-st stage were eaten, who were on a water surface a lot of time. Active pursuit of individuals of young stage isn’t characteristic for 4-th stage larvae. Large larvae absorb small individuals by a water surface filtration. The food gets to a mouth with water current which is set by specific movement of the upper and lower jaws [4].
Observations showed that 1-st stage larvae are for the most part in water column by a bottom of the vessel without access to atmospheric air even through the external stimulus doesn’t take action on them, and there is a food on the water surface. Larvae of advanced stages, on the contrary, usually swim on the water surface where the filtration is carried out. They have reaction of the submersion more often because of fright or a lack of food. Thus they remain on depth insignificant time: from several seconds to several minutes.
It is experimentally shown that the heightened ability to long integumentary and branchial breath is character for 1-st stage larvae and this ability allows them to keep viability without access to atmospheric air about several days. Besides, observations after behavior of 1-st stage individuals found to assert that the food from an underwater substratum is the basic way getting of food for them, unlike larvae of advanced stages. In our opinion, origin and fixation of two interconnected adaptations - physiological and behavioural - allow larvae of young stage to reduce probability of death because of cannibalism of larvae of advanced stages.
As it has been noted above, 4-th stage larvae prefer to eat in norm without diving from water surface, but if the food is not enough they dive and eat round the substratum under water.
It is shown that specialization of getting of various kind of food is connected with morphological parameters of larvae head [5]. The head index is used for a
rating of these parameters - the relation of the greatest width of a head to its length. Larvae that specialize on a filtration of particles by water surface have wider head and a great value of the head index. Individuals, more often eating round an underwater substratum, have opposite characteristics.
Both by the heightened density and by a lack of forage larvae pass from a filtration to the scraping from substratum more actively. It is interesting that behavioural effect is the same, both the conditions of high density of the keeping, but when the forage is enough and by reduction of food concentration in the environment.
Thus, it is possible to suppose that plasticity of strategy of getting of food by larvae Anopheles is defined by various factors of environment, and their reaction connected with transition to an additional way of getting of food, can be the nonspecific answer on stressful influence.
It is emphasized in work by S. P. Rasnitsyn, V. V. Jasjukevich [6] that individuals of different kinds Anopheles can switch over the filtration to alternative type of nutrition in different ways, diving on depth. Moreover, in the opinion of these researchers, getting of the forage from an underwater substratum is absolutely not peculiar to A. atroparvus more deeply body length of the individual, and even on advanced stages.
Our observation at behavior preimaginales stages of development A. atroparvus conflicts with this material. It was noticed at the keeping in a laboratory line that larvae of all stages sank on a bottom of a vessel for a food regularly at depth of water about 5 cm, especially in the conditions of high density and deficiency of forage on a water surface. Considering it quantity in 6 cm was chosen like the initial height of a liquid column in the first repeatability of experiment.
It is necessary to notice that this test was carried out two times as results were inconsistent in its first series. Calculation of quantity of scrapings from the bottom at depth of 6 cm was begun in 10 min after transference of larvae in the vessel. 54 attempts of feeding from the bottom were fixed during follow-up 10 min. The same larvae dived 81 times on depth of 8 cm during the following 10 min, and then on 10 cm -already 96 times (Fig. 2, a dashed line). And then, the quantity of attempts of scraping from the bottom decreased as the natural result when consecutive increasing of water depth in the vessel.
It turned out as if frequency of achievement of a bottom by larvae is less at smaller depth - 6 sm and 8 sm - than at a deep water. We made the assumption that it was because of time lack (10 min), which it is necessery for an exit of individuals from stress in the time of their transference in an experimental vessel.
That’s why we increased time of primary habit of larvae to the vessel to 35 min in the second series of
i И- *1 i >—
У /
I <
6 S 10 12 14 16 18
h. cm
Fig. 2. Dependence of quantity of dives for a food from the bottom by larvae Anopheles atroparvus on water depth. Conventional signs: h -height of a liquid column in a vessel; n - quantity of dives on a bottom during 10 min
experiment and only then we began to make calculation of the dives accompanied by feeding from the bottom. In this case the quantity of dives at first two depths (6 and 8 cm) increased and was practically compared to indicators at depth of 10 cm (it is full line on Fig. 2). Thus, our assumption is confirmed: the stressful condition inhibits food behavior of larvae, and time which is equal of 10 min, is insufficient to exit from it.
Thus, it is shown for A. atroparvus that the greatest quantity of dives for feeding is at depths of 10 cm, and this quantity is relatively constant. And then the quantity of dives to the bottom is reduced gradually and naturally at increase of water depth in a vessel.
On the ground of results of experiment it is possible to calculate coefficients of a feeding from an underwater substratum (q) on one larva depending on level of height of a liquid column in unit of time, using the formula:
q = Q / n * T,
where Q is quantity of dives for a feeding during time T, n is quantity of considered larvae.
The quantity of dives of 4-th stage larvae A. atroparvus for scraping from the bottom of the vessel has the going down linear nature since 10 cm (Table).
Coefficients offeeding from an underwater substratum of larvae A. atroparvus in unit of time (q) depending on water depth
Water depth, cm Q for 10 min q
6 93 0.186
8 97 0.194
10 96 0.192
12 86 0.172
14 77 0.154
16 52 0.104
18 34 0.068
The note: q is calculated for the second series of experiment - accustoming of larvae to vessel during 35 min.
Thus, results of experiments are evidence of larvae young and advanced stages Anopheles have various trophic and spatial niches in reservoirs. And so we can explain the big ability of 1-st stage larvae to be in the water column without access to atmospheric air (about several days at water temperatures of 15-23 °C) and it is an important component of their adaptive complex. Thus it is reached decrease of a food competition between stages and pressure of cannibalism on larvae of young stages. At the same time, individuals of advanced stages A. atroparvus dive actively on depth of tens of centimeters in search of food and use alternative type of a feeding - feed from an underwater substratum.
References
1. Beklemishev V. N. Ecology of Malarial Mosquitoes. М.: Medgiz, 1944. 299 p.
2. Gordeev М. I., Sibataev А. К. Age-specific selection and ability to cannibalism of malarial mosquitoes' larvae with different karyotypes // Genetics.
1995а. Т. 31. № 7. P. 939-946.
3. Gordeev М. I., Troshkov N. Y Inversion polymorphism of malarial mosquito Anopheles messeae. Presentation IX. Cannibalism of larvae as a
selective factor // Genetics. 1990. T. 26. № 9. P. 1597-1603.
4. Monchadsky A. S. Larvae of Bloodsucking Mosquitoes USSR and Adjacent Countries (Subfamily Culicinae). М.: Publishing House: AS USSR, 1951. 290 p.
5. Burlak V. А., Sibataev А. К., Perevozkin V. P., Gordeev М. I. Interconnection between food behavior of larvae of two species of malarial mosquitoes
and their inversion genotype // Ecology. 1999. № 5. P. 379-381.
6. Rasnitsyn S. P., Yasyukevich V. V. Connection of food way of malarial mosquitoes' larvae with their texture and behavior // Zool. mag. 1989. T. 68.
№ 7. P. 155-157.
Perevozkin V. P
Tomsk State Pedagogical University.
Ul. Kievskaya, 60, Tomsk, Russia, 634061.
Tomsk State University.
Pr. Lenina, 36, Tomsk, Russia, 634050.
E-mail: pvptomsk@rambler.ru
Galkin V. S.
Tomsk State Pedagogical University.
Ul. Kievskaya, 60, Tomsk, Russia, 634061.
E-mail: vitalygalkin2008@rambler.ru
Received 14.03.2011.
В. П. Перевозкин, В. С. Галкин
АЛЬТЕРНАТИВНЫЕ СПОСОБЫ ПИТАНИЯ ЛИЧИНОК МАЛЯРИЙНЫХ КОМАРОВ (DIPTERA, CULICIDAE)
КАК ВАЖНЫЕ СОСТАВЛЯЮЩИЕ ИХ АДАПТИВНЫХ КОМПЛЕКСОВ
Были изучены особенности поведения личинок малярийных комаров Anopheles atroparvus (Diptera, Culicidae), связанные с дополнительными способами добывания пищи - обскребыванием субстрата и каннибализмом. Результаты экспериментов свидетельствуют о том, что личинки младших и старших возрастов Anopheles имеют в биотопах различные трофические и пространственные ниши. При этом достигается понижение пищевой конкуренции между возрастами и давления каннибализма на личинок младших возрастов.
В то же время особи старших возрастов A. atroparvus активно ныряют на глубину десятков сантиметров в поисках корма, переключаясь на альтернативный тип питания - обскребывание.
Ключевые слова: малярийные комары, стадии развития, типы питания, каннибализм, обскребывание, поведение, конкуренция.
Перевозкин В. П., кандидат биологических наук, доцент, старший научный сотрудник.
Томский государственный педагогический университет.
Ул. Киевская, 60, Томск, Россия, 634061.
Томский государственный университет.
Пр. Ленина, 36, Томск, Россия, 634050.
E-mail: pvptomsk@rambler.ru
Галкин В. С., аспирант.
Томский государственный педагогический университет.
Ул. Киевская, 60, Томск, Россия, 634061.
E-mail: vitalygalkin2008@rambler.ru
