Does cognitive ability always correlate with a positive fitness consequence? Previous research in both vertebrates and invertebrates provides mixed results. Here, we compare the learning and memory abilities of Africanized honeybees ( Apis mellifera scutellata hybrid) and European honeybees ( Apis mellifera ligustica). The range of the Africanized honeybee continues to expand, superseding the European honeybee, which led us to hypothesize that they might possess greater cognitive capabilities as revealed by a classical conditioning assay. Surprisingly, we found that fewer Africanized honeybees learn to associate an odor with a reward. Additionally, fewer Africanized honeybees remembered the association a day later.
While Africanized honeybees are replacing European honeybees, our results show that they do so despite displaying a relatively poorer performance on an associative learning paradigm. IntroductionLearning, defined as an animal’s behavioral adjustment based on previous experience, is traditionally assumed to confer some positive benefit on the animal’s fitness. Learning should potentially help an organism in many contexts, such as selecting a superior nest site (; ), recognizing individuals that “owe” an altruistic benefit , singing a better song to attract mates , foraging for higher quality (;; ) and quantity of food, or learning cues from conspecifics to avoid predation. However, while previous research has focused on these adaptive benefits of learning, there is little experimental evidence to show that superior learning abilities might directly benefit an animal competing with another animal. This issue is especially interesting when the animals are closely related as this usually results in niche overlap and therefore, competition for the same resources with competitors using similar physical and behavioral traits.Honeybees are a well-established, invertebrate model for the study of learning, which is a key attribute important for the competitive exploitation of floral resources.
The largest Naruto Forums and community based on the Naruto anime and manga series. Discuss all things Naruto, including the latest anime and manga releases! Africanized Bee Stings. Africanized killer bee venom is no more dangerous than that of regular honeybees. However, these bees tend to attack in greater numbers, which causes more danger to humans. If under attack by an Africanized honeybee, run quickly away in a zig zag pattern and seek shelter indoors or in a car as soon as possible.
Bees must learn to associate a location of a foraging site with numerous characteristics and remember profitable sites from day to day (; ). As appetitive learning is a robust and rapidly occurring phenomenon in bees (; ), it has been an important laboratory tool in learning research for over 50 years (; ).Honeybees ( Apis mellifera) have been managed by humans for thousands of years. While most European honeybee (EHB) subspecies are relatively docile, native African honeybees ( Apis mellifera scutellata) are more aggressive. African honeybees were introduced into Brazil in 1956 where they were hybridized with the present EHBs to produce “Africanized” honeybees (AHBs; ), also known as “killer bees.” Previous studies have focused on agricultural aspects identification (;; ), life history , honey production , pollination , and response to insecticides and their infamous defensive behavior (; ). Despite their public fame, relatively little research has been conducted on their cognitive capabilities.
It was shown that AHBs are good laboratory subjects, capable of training in a classical conditioning paradigm to associate various odors and other stimuli with a reward (; ).AHBs are ecologically successful, superseding EHBs throughout Central America and southern USA (;;; ). Their range continues to expand. As AHBs have outcompeted EHBs, we wished to compare the cognitive abilities of the two to see if superior learning performance of AHBs might correlate with ecological success. Additionally, domesticated animals usually have reduced cognitive abilities compared to their wild con-specifics , which would also lead us to hypothesize the “feral” AHB to perform better in learning assays than the more “domesticated” EHB.Here, we compare the performance of EHBs and AHBs in a standard learning paradigm where bees learned to associate an odor (jasmine) with a sugar reward (sucrose solution). We hypothesize that there may be differences in the learning ability between the two races of honeybee (EHB and AHB) that could confer a fitness advantage.
European honeybees (EHB; b, red) perform better in a learning assay compared to Africanized honeybees (AHB; c, gray). Data ( a) represent percentage of bees of each race demonstrating a learned associative response (proboscis extension) to an odor (jasmine) for trials 1–7. Odors (CS) used were either jasmine ( boxplots—data pooled for colonies) or lily of the valley ( triangles; n=30 bees from one colony). Boxes represent interquartile ranges (25–75%) with the median marked, and whiskers indicate 10–90%. Coloration of bees ( b, c) might differ under field conditions. Study organisms and collection of beesThe European honeybee (predominantly Apis mellifera ligustica) colonies used in this study were headed by commercially reared queens (Big Island Queens in Captain Cook, Hawaii) that were mated in Hawaii where only EHBs are present.
The Africanized honeybee colonies ( A. Scutellata hybrids) were collected from swarms in Tucson, Arizona, USA, as southern Arizona is home to a feral population of Africanized bees (;;; ). Both colonies of EHBs and AHBs are maintained at the United States Department of Agriculture Carl Hayden Bee Laboratory in Tucson, Arizona, USA. All colonies were queenright and housed in either a standard Langstroth hive of at least one deep box or a smaller mating nucleus hive. All colonies had a visible entrance from which we were able to observe returning foragers and collect bees.As sucrose responsiveness and associative learning differ between the different types of foragers (nectar/pollen/water;; ), we collected returning foragers without pollen loads outside the entrance of their colony.
We made six collecting trips between December 7, 2007 and January 30, 2008, and on each trip, we selected a different AHB and EHB colony, making a total of 12 different colonies, six of each race. We tested a total of 232 bees with an average of 18.2 AHBs (±0.6 SE) and 20.5 EHBs (±0.4 SE) per colony/collecting trip.Bees were transported back to the laboratory where they were chilled and mounted in plastic tubes. At this point, we verified that sample bees demonstrated a clear proboscis extension to the reward solution (50% v/v sucrose in water) as a basic requirement for the conditioning procedure. Such a high concentration sucrose solution is easily perceived by a human observer and considerably higher than reported thresholds for honeybees. Immobilized bees were fed to satiation at 17:00 h and then left without food overnight, as it is important in any learning protocol to account for appetitive motivation. There was no noticeable behavioral difference between the two races of bees in the testing apparatus (i.e., one race did not appear stressed), as was previously reported. Both races showed seemingly similar respiration rates and were able to feed until satiation.
Additionally, AHBs had previously been shown to demonstrate reliable gustory responsiveness and odor discrimination using this classical conditioning assay , so we felt confident that neither race was adversely affected by the training regime. Data collection began at approximately 10:00 h the next morning.
Data collection—associative learning by proboscis extension reflexThe next morning, bees were trained in a standard paradigm of classical conditioning (; ) where a jasmine-laden air current (conditioned stimulus, CS) was presented for 5 s; a vacuum removed the olfactory stimulus from the training area (flow rate ca. AHBs, like EHBs, are capable of associatively learning a variety of odors. We chose a floral odor because honeybees use them as a cue to distinguish between flower species when foraging. Also, we repeated this experiment with an additional EHB/AHB colony pair ( n=30 bees total) using another floral odor as CS (lily of the valley).The antennae were touched with a toothpick soaked in the sucrose solution (unconditioned stimulus, US) 3 s after odor onset, upon which the bees reflexively extended their proboscis to receive the reward (unconditioned response). Bees that spontaneously responded to the first odor presentation or that did not respond with a proboscis extension reflex to the first sucrose stimulus were discarded, as both sets of bees would be untrainable in the forward pairing of an odor with a reward; however, this was an infrequent occurrence. For the entire experiment, only a total of four (4%) AHBs and three (2.7%) EHBs were discarded for the former reason and eight (8%) AHBs and ten (8.8%) EHBs for the latter reason.After 30 min, bees were submitted to another training cycle of successive presentation of CS and US.
This was repeated seven times, a training regime similar to the spaced protocol used in learning studies with Drosophila (; ). Bees responding with a proboscis extension during the first 3 s of the odor presentation before the sucrose application to the antennae were considered as having showed the correct Proboscis Extension Reflex (PER). AHBs and EHBs were tested in random order to account for different levels of hunger/motivation, and the tester was blind to the race of the bee. Data collection—weight and size distribution of workersAs learning generally correlates with body size across species , we wished to see if a difference in size between the two bee races might correlate with PER performance. After the memory trial, we chilled each bee and measured her head width with digital calipers to the nearest hundredth millimeters under magnification of 8×. We weighed each bee using a digital scale (Scientech SA80), which was calibrated to the nearest 0.1 mg. Furthermore, we weighed the bee with the abdomen removed to minimize any potential variation from the volume of fluid in the crop.
Statistical analysesAll statistics were performed using Minitab (Student version 14). To analyze differences in learning and memory between AHBs and EHBs, we used a binary logistic regression because our response variable was yes/no (PER or no PER). Additionally, we expected the data, as it is learning data, to fit a nonlinear function, which is permissible in this model.The model analyzed the response variable against the factors of race (AHB versus EHB), colony (1–12), and trials (1–7) as well as interactions between factors like race and trial. We did not include the factor of day in the model because of redundancy—we would expect “colony” and “day” to covary completely because each day we selected two new colonies, one of each race. However, for both learning and retention data, we reran models substituting “day” for “colony” to confirm that significance levels that remained the same.Size data were analyzed using analysis of variance (ANOVA) and potential correlations between size and learning was determined using Pearson’s correlations. More EHBs than AHBs learned the odor associationIn every trial, a significantly larger percentage of EHBs showed a learned proboscis response to the odor (CS) compared to the AHBs (binary logistic regression model, odds ratio=0.43, p. More EHBs than AHBs remembered the odor associationIn addition to comprising a higher proportion of learners, EHBs also displayed significantly superior retention of learned associations between the odor and the reward after 24 h (79% of EHBs versus 51% of AHBs, binary logistic regression model, odds ratio=0.36, p=0.001; ).
Retention was considered for bees that had previously showed the learned association (PER to two or more of the seven learning trials). Colony/day (binary logistic regression model, odds ratio=0.85, p=0.642) were nonsignificant factors. Additionally, this significance was maintained when we reran this analysis using different thresholds for learning: for bees displaying PER to four or greater of seven learning trials, a significantly higher number of EHBs retained the learned association after 24 h with the jasmine odor than for AHBs (88% EHBs versus 69% AHBs, binary logistic regression model, odds ratio=0.33, p=0.02). Colony/day remained nonsignificant factors (binary logistic regression model, odds ratio=0.90, 1.01, p=0.82, 0.76). EHBs are larger than AHBs; however, size and learning do not correlateAs previously reported (; ), EHBs were significantly larger than AHBs: mean head width (3.71 mm versus 3.66 mm, n=113, 100, SE=0.0072, 0.0087; one-way ANOVA, F 1,211=20.78, p.
DiscussionOur study compared the learning and memory of Africanized and European honeybees in a classical conditioning assay where the bee learns to associate a stimulus with a reward. Surprisingly, a consistent and significant smaller proportion of AHBs than EHBs learned the association ( p.
Does cognitive ability always correlate with a positive fitness consequence? Previous research in both vertebrates and invertebrates provides mixed results. Here, we compare the learning and memory abilities of Africanized honeybees ( Apis mellifera scutellata hybrid) and European honeybees ( Apis mellifera ligustica). The range of the Africanized honeybee continues to expand, superseding the European honeybee, which led us to hypothesize that they might possess greater cognitive capabilities as revealed by a classical conditioning assay.
Surprisingly, we found that fewer Africanized honeybees learn to associate an odor with a reward. Additionally, fewer Africanized honeybees remembered the association a day later. While Africanized honeybees are replacing European honeybees, our results show that they do so despite displaying a relatively poorer performance on an associative learning paradigm. IntroductionLearning, defined as an animal’s behavioral adjustment based on previous experience, is traditionally assumed to confer some positive benefit on the animal’s fitness.
Learning should potentially help an organism in many contexts, such as selecting a superior nest site (; ), recognizing individuals that “owe” an altruistic benefit , singing a better song to attract mates , foraging for higher quality (;; ) and quantity of food, or learning cues from conspecifics to avoid predation. However, while previous research has focused on these adaptive benefits of learning, there is little experimental evidence to show that superior learning abilities might directly benefit an animal competing with another animal. This issue is especially interesting when the animals are closely related as this usually results in niche overlap and therefore, competition for the same resources with competitors using similar physical and behavioral traits.Honeybees are a well-established, invertebrate model for the study of learning, which is a key attribute important for the competitive exploitation of floral resources.
Bees must learn to associate a location of a foraging site with numerous characteristics and remember profitable sites from day to day (; ). As appetitive learning is a robust and rapidly occurring phenomenon in bees (; ), it has been an important laboratory tool in learning research for over 50 years (; ).Honeybees ( Apis mellifera) have been managed by humans for thousands of years. While most European honeybee (EHB) subspecies are relatively docile, native African honeybees ( Apis mellifera scutellata) are more aggressive. African honeybees were introduced into Brazil in 1956 where they were hybridized with the present EHBs to produce “Africanized” honeybees (AHBs; ), also known as “killer bees.” Previous studies have focused on agricultural aspects identification (;; ), life history , honey production , pollination , and response to insecticides and their infamous defensive behavior (; ). Despite their public fame, relatively little research has been conducted on their cognitive capabilities.
It was shown that AHBs are good laboratory subjects, capable of training in a classical conditioning paradigm to associate various odors and other stimuli with a reward (; ).AHBs are ecologically successful, superseding EHBs throughout Central America and southern USA (;;; ). Their range continues to expand. As AHBs have outcompeted EHBs, we wished to compare the cognitive abilities of the two to see if superior learning performance of AHBs might correlate with ecological success. Additionally, domesticated animals usually have reduced cognitive abilities compared to their wild con-specifics , which would also lead us to hypothesize the “feral” AHB to perform better in learning assays than the more “domesticated” EHB.Here, we compare the performance of EHBs and AHBs in a standard learning paradigm where bees learned to associate an odor (jasmine) with a sugar reward (sucrose solution).
We hypothesize that there may be differences in the learning ability between the two races of honeybee (EHB and AHB) that could confer a fitness advantage. European honeybees (EHB; b, red) perform better in a learning assay compared to Africanized honeybees (AHB; c, gray). Data ( a) represent percentage of bees of each race demonstrating a learned associative response (proboscis extension) to an odor (jasmine) for trials 1–7.
Odors (CS) used were either jasmine ( boxplots—data pooled for colonies) or lily of the valley ( triangles; n=30 bees from one colony). Boxes represent interquartile ranges (25–75%) with the median marked, and whiskers indicate 10–90%. Coloration of bees ( b, c) might differ under field conditions. Study organisms and collection of beesThe European honeybee (predominantly Apis mellifera ligustica) colonies used in this study were headed by commercially reared queens (Big Island Queens in Captain Cook, Hawaii) that were mated in Hawaii where only EHBs are present. The Africanized honeybee colonies ( A. Scutellata hybrids) were collected from swarms in Tucson, Arizona, USA, as southern Arizona is home to a feral population of Africanized bees (;;; ). Both colonies of EHBs and AHBs are maintained at the United States Department of Agriculture Carl Hayden Bee Laboratory in Tucson, Arizona, USA.
All colonies were queenright and housed in either a standard Langstroth hive of at least one deep box or a smaller mating nucleus hive. All colonies had a visible entrance from which we were able to observe returning foragers and collect bees.As sucrose responsiveness and associative learning differ between the different types of foragers (nectar/pollen/water;; ), we collected returning foragers without pollen loads outside the entrance of their colony. We made six collecting trips between December 7, 2007 and January 30, 2008, and on each trip, we selected a different AHB and EHB colony, making a total of 12 different colonies, six of each race.
We tested a total of 232 bees with an average of 18.2 AHBs (±0.6 SE) and 20.5 EHBs (±0.4 SE) per colony/collecting trip.Bees were transported back to the laboratory where they were chilled and mounted in plastic tubes. At this point, we verified that sample bees demonstrated a clear proboscis extension to the reward solution (50% v/v sucrose in water) as a basic requirement for the conditioning procedure. Such a high concentration sucrose solution is easily perceived by a human observer and considerably higher than reported thresholds for honeybees. Immobilized bees were fed to satiation at 17:00 h and then left without food overnight, as it is important in any learning protocol to account for appetitive motivation. There was no noticeable behavioral difference between the two races of bees in the testing apparatus (i.e., one race did not appear stressed), as was previously reported. Both races showed seemingly similar respiration rates and were able to feed until satiation. Additionally, AHBs had previously been shown to demonstrate reliable gustory responsiveness and odor discrimination using this classical conditioning assay , so we felt confident that neither race was adversely affected by the training regime.
Data collection began at approximately 10:00 h the next morning. Data collection—associative learning by proboscis extension reflexThe next morning, bees were trained in a standard paradigm of classical conditioning (; ) where a jasmine-laden air current (conditioned stimulus, CS) was presented for 5 s; a vacuum removed the olfactory stimulus from the training area (flow rate ca. AHBs, like EHBs, are capable of associatively learning a variety of odors. We chose a floral odor because honeybees use them as a cue to distinguish between flower species when foraging.
Also, we repeated this experiment with an additional EHB/AHB colony pair ( n=30 bees total) using another floral odor as CS (lily of the valley).The antennae were touched with a toothpick soaked in the sucrose solution (unconditioned stimulus, US) 3 s after odor onset, upon which the bees reflexively extended their proboscis to receive the reward (unconditioned response). Bees that spontaneously responded to the first odor presentation or that did not respond with a proboscis extension reflex to the first sucrose stimulus were discarded, as both sets of bees would be untrainable in the forward pairing of an odor with a reward; however, this was an infrequent occurrence.
For the entire experiment, only a total of four (4%) AHBs and three (2.7%) EHBs were discarded for the former reason and eight (8%) AHBs and ten (8.8%) EHBs for the latter reason.After 30 min, bees were submitted to another training cycle of successive presentation of CS and US. This was repeated seven times, a training regime similar to the spaced protocol used in learning studies with Drosophila (; ). Bees responding with a proboscis extension during the first 3 s of the odor presentation before the sucrose application to the antennae were considered as having showed the correct Proboscis Extension Reflex (PER). AHBs and EHBs were tested in random order to account for different levels of hunger/motivation, and the tester was blind to the race of the bee. Data collection—weight and size distribution of workersAs learning generally correlates with body size across species , we wished to see if a difference in size between the two bee races might correlate with PER performance.
After the memory trial, we chilled each bee and measured her head width with digital calipers to the nearest hundredth millimeters under magnification of 8×. We weighed each bee using a digital scale (Scientech SA80), which was calibrated to the nearest 0.1 mg. Furthermore, we weighed the bee with the abdomen removed to minimize any potential variation from the volume of fluid in the crop. Statistical analysesAll statistics were performed using Minitab (Student version 14).
To analyze differences in learning and memory between AHBs and EHBs, we used a binary logistic regression because our response variable was yes/no (PER or no PER). Additionally, we expected the data, as it is learning data, to fit a nonlinear function, which is permissible in this model.The model analyzed the response variable against the factors of race (AHB versus EHB), colony (1–12), and trials (1–7) as well as interactions between factors like race and trial. We did not include the factor of day in the model because of redundancy—we would expect “colony” and “day” to covary completely because each day we selected two new colonies, one of each race. However, for both learning and retention data, we reran models substituting “day” for “colony” to confirm that significance levels that remained the same.Size data were analyzed using analysis of variance (ANOVA) and potential correlations between size and learning was determined using Pearson’s correlations. More EHBs than AHBs learned the odor associationIn every trial, a significantly larger percentage of EHBs showed a learned proboscis response to the odor (CS) compared to the AHBs (binary logistic regression model, odds ratio=0.43, p. More EHBs than AHBs remembered the odor associationIn addition to comprising a higher proportion of learners, EHBs also displayed significantly superior retention of learned associations between the odor and the reward after 24 h (79% of EHBs versus 51% of AHBs, binary logistic regression model, odds ratio=0.36, p=0.001; ). Retention was considered for bees that had previously showed the learned association (PER to two or more of the seven learning trials).
Colony/day (binary logistic regression model, odds ratio=0.85, p=0.642) were nonsignificant factors. Additionally, this significance was maintained when we reran this analysis using different thresholds for learning: for bees displaying PER to four or greater of seven learning trials, a significantly higher number of EHBs retained the learned association after 24 h with the jasmine odor than for AHBs (88% EHBs versus 69% AHBs, binary logistic regression model, odds ratio=0.33, p=0.02). Colony/day remained nonsignificant factors (binary logistic regression model, odds ratio=0.90, 1.01, p=0.82, 0.76). EHBs are larger than AHBs; however, size and learning do not correlateAs previously reported (; ), EHBs were significantly larger than AHBs: mean head width (3.71 mm versus 3.66 mm, n=113, 100, SE=0.0072, 0.0087; one-way ANOVA, F 1,211=20.78, p. DiscussionOur study compared the learning and memory of Africanized and European honeybees in a classical conditioning assay where the bee learns to associate a stimulus with a reward.
Surprisingly, a consistent and significant smaller proportion of AHBs than EHBs learned the association ( p.