_{1}

^{*}

Samples of workers of honeybee were collected from 42 colonies in 13 localities in the Lake Chad Basin (parts of Cameroon, Chad, and Nigeria) and analysed using classical morphometry. Measurements of 35 morphological characters of body size, colour and pilosity were taken from 10 workers per colony and the data subjected to one-way analysis of variance (ANOVA), principal components analysis (PCA), hierarchical cluster analysis (HCA), stepwise discriminant analysis (DA) and Pearson’s product-moment correlation analysis. A one-way ANOVA revealed that means of 21 of the morphometric characters differed significantly (p < 0.05) among sampled localities while means of the remaining 14 characters did not (p > 0.05). The bees formed one cluster in a PCA. However, scatter plots of altitude against principal component 1 of PCA (loaded with characters of body size) revealed an increase of size of the bees along the gradient of the Lake Chad Basin. The coefficient of determination (R2) indicated that 88% and 77% of the variation in size might be explained by altitude in the southeastern and southwestern parts of the basin, respectively. Additionally, there was a very highly significant strong positive relationship between principal component 1 and altitude (r(30) = 0.618, p < 0.0005). Similarly, HCA and DA classified the colonies into three morphoclusters whose distribution closely followed the altitude of the area.

Honeybees are of considerable economic importance, producing products of commercial value, such as honey and wax, and pollinating crops and wild plants. For example, Calderone [

The natural range of the western honeybee, A. mellifera, is western Asia, Africa and Europe: From southern Scandinavia in the north to the Cape of Good Hope in the south, from Dakar in the west to the Urals, Mashhad and to the coast of Oman in the East. Geographical isolation and ecological adaptations resulted in the evolution of local populations showing considerable geographical variation, resulting in adaptation to local factors of climate, vegetation, pests and pathogens [

The area of study (

Most of the area lies in the Guinea and Sudan savanna zones though the lake itself lies in the Sahel, a transitional zone between savanna and desert.

The savannas consist of a mixture of grasslands and woody vegetation; moderate rainfall with a short rainy season (less than half of the year); and a high variation of mean annual temperature (10˚C to 15˚C). The density of vegetation, species richness, amount of rainfall and length of the rainy season decrease with the increase in latitude. Annuals flower at the end of the rainy season while trees flower during the dry season.

The Sahel is characterized by scanty rainfall; very short rainy season; very sparse vegetation of short trees and grass; and frequent droughts.

Altitude varies from 280 metres above sea level on the shores of the lake to about 1300 metres on the Jos Plateau.

Samples of workers of honeybee were collected from 42 colonies in 13 localities in Chad, Cameroon and Nigeria (

Morphometric measurements of 35 characters were taken from 10 bees from each colony according to Ruttner [

First, the mean and standard deviation of each of the 35 morphometric characters were calculated for every colony. Then the means for colonies were used to calculate the means and standard deviations for localities. The data were subjected to a one-way analysis of variance (ANOVA) to compare different localities. Tukey HSD tests, on the means of the 35 characters, were used to detect significant differences between the localities. The level of statistical significance chosen was p = 0.05.

Locality | Country | Latitude (˚N) | Longitude (˚E) | Altitude (m) | Number of Colonies |
---|---|---|---|---|---|

Maga | Cameroon | 10.51 | 14.93 | 320 | 5 |

Touboro | Cameroon | 7.78 | 15.37 | 1213 | 5 |

N'Djamena | Chad | 12.10 | 15.08 | 298 | 3 |

Am Timan | Chad | 11.03 | 20.30 | 439 | 3 |

Bousso | Chad | 10.50 | 16.70 | 337 | 4 |

Sarh | Chad | 9.15 | 18.38 | 369 | 2 |

Koumra | Chad | 8.90 | 17.60 | 411 | 1 |

Moundou | Chad | 8.60 | 16.08 | 400 | 4 |

Afunori | Nigeria | 13.70 | 13.33 | 283 | 5 |

Maiadua | Nigeria | 13.18 | 8.23 | 469 | 3 |

Bauchi | Nigeria | 10.32 | 9.83 | 620 | 2 |

Mubi (Salmakoli) | Nigeria | 10.02 | 13.10 | 518 | 4 |

Jos (Laminga) | Nigeria | 9.83 | 8.98 | 1332 | 2 |

Ruttner No. | Character | |
---|---|---|

A. Hair | ||

1 | Length of cover hair on tergite 5 | |

2 | Width of the tomentum band on the side of tergite 4 | |

3 | Width of the dark stripe between the tomentum and the posterior rim of the tergite | |

B. Size | ||

5 | Femur, length | |

6 | Tibia, length | |

7 | Metatarsus, length | |

8 | Metatarsus, width | |

9 | Tergite 3, longitudinal diameter | |

10 | Tergite 4, longitudinal diameter | |

11 | Sternite 3, longitudinal diameter | |

12 | Wax plate(mirror) of sternite 3, longitudinal diameter | |

13 | Wax plate of sternite 3, transversal diameter | |

14 | Distance between wax plates of sternite 3 | |

15 | Sternite 6, longitudinal diameter | |

16 | Sternite 6, transversal diameter | |

C. Fore-wing | ||

17 | Fore-wing, length | |

18 | Fore-wing, width | |

19 | Cubital vein, distance a | |

20 | Cubital vein, distance b | |

21-31 | 11 angles of wing venation | |

(No. 21 = A4, 22 = B4, 23 = D7, 24 = E19, 25 = G18, 26 = J10, 27 = J16, 28 = K19, 29 = L13, 30 = N23, 31 = O26) | ||

D. Colour | ||

32 | Pigmentation of tergite 2 | |

33 | Pigmentation of tergite 3 | |

34 | Pigmentation of tergite 4 | |

35 | Pigmentation of scutellum (Sc) | |

36 | Pigmentation of plates of scutellum (B, K) |

A PCA, using colony means of 35 morphometric characters was run in order to detect any possible clusters. The suitability of PCA was assessed, prior to the analysis, using correlation coefficients of the variables, Kaiser- Meyer-Olkin (KMO) measure of sampling adequacy and Bartlett’s test of sphericity [

Then a hierarchical cluster analysis was carried out with the assumption that samples from each locality formed a distinct population. Thus, 13 populations were assumed and the analysis was carried out using the means of the 35 morphometric characters for the 13 localities in the study.

A stepwise discriminant analysis (DA) was run in order to confirm the groups predicted by cluster analysis and to determine the discriminant characters. The suitability of DA was determined through log determinants and Box’s M test. In DA the basic assumption is that the variance-co-variance matrices are equivalent. For this assumption to hold the log determinants should be equal and the Box’s M test should not be significant. The latter tests the null hypothesis that the covariance matrices do not differ between groups formed by the dependent variable. Wilk’s lambda was used to test the discriminatory power of the discriminant functions while the significance of the distance between group centroids was tested by F-statistic.

A Pearson’s product-moment correlation analysis was run to assess the relationship between latitude, longitude and altitude and principal component 1 extracted by PCA (representing morphological characters loaded on it). Prior to analysis, the data were assessed for linearity, normal distribution and presence of outliers [

All statistical analyses were carried out with IBM^{®} SPSS^{®} Statistics Version 20 with additional material from Burns and Burns [

Means of the 35 morphometric characters for the sampled localities are given in Tables 3-6.

A one-way ANOVA revealed that means of 21 of the morphometric characters (length of cover hair on tergite 5, width of the tomentum band on the side of tergite 4, width of the dark stripe between the tomentum and the posterior rim of the tergite, length of femur, length of tibia, length of metatarsus, width of metatarsus, longitudinal diameter of tergites 3 and 4, longitudinal diameter of sternite 3, transversal diameter of wax plate of sternite 3, transversal diameter of sternite 6, length of fore-wing, five angles of wing venation (D7, E19, J16, K19 and N23), pigmentation of tergite 3, pigmentation of scutellum and pigmentation of plates of scutellum) differed significantly (p < 0.05) between sampled localities while means of the remaining 14 characters (pigmentation of the second and fourth tergites, longitudinal diameter of wax plate (mirror) of sternite 3, distance between wax mirrors of sternite 3, longitudinal diameter of sternite 6, width of fore-wing, the two cubital distances, and angles A4, B4, G18, J10, L13, and 026) did not (p > 0.05).

In order to investigate the similarity of the honeybee colonies under study, a PCA, using colony means of six morphometric characters (29 characters were excluded from the analysis during a preliminary PCA due to their

Locality | N | Hair(1)^{***} | Tom1(2)^{***} | Tom2(3)^{*} | Pt2(32)^{†} | Pt3(33)^{**} | Pt4(34)^{†} | Scut1(35)^{***} | Scut2(36)^{***} |
---|---|---|---|---|---|---|---|---|---|

Maga | 5 | 0.13c | 0.68ab | 0.48a | 9.00 | 8.16c | 4.02 | 7.56c | 5.12d |

0.02 | 0.02 | 0.02 | 0.00 | 0.23 | 0.04 | 0.30 | 0.52 | ||

Touboro | 4 | 0.18e | 0.62a | 0.47a | 8.97 | 7.94bc | 3.98 | 6.51ab | 3.67abcd |

0.02 | 0.05 | 0.03 | 0.06 | 0.00 | 0.05 | 0.31 | 0.81 | ||

N'Djamena | 3 | 0.10ab | 0.69abc | 0.48a | 9.00 | 8.00bc | 4.00 | 7.60c | 4.63cd |

0.01 | 0.02 | 0.02 | 0.00 | 0.00 | 0.00 | 0.17 | 0.38 | ||

Am Timan | 3 | 0.13bc | 0.67ab | 0.44a | 9.00 | 8.00bc | 4.00 | 6.20a | 2.15a |

0.01 | 0.05 | 0.01 | 0.00 | 0.00 | 0.00 | 0.49 | 0.05 | ||

Bousso | 4 | 0.15cd | 0.67ab | 0.45a | 9.00 | 8.09bc | 4.00 | 6.40a | 3.33abc |

0.01 | 0.04 | 0.02 | 0.00 | 0.11 | 0.00 | 0.41 | 0.14 | ||

Sarh | 2 | 0.14cd | 0.75bc | 0.45a | 9.00 | 7.25a | 4.13 | 6.87abc | 3.63abcd |

0.00 | 0.03 | 0.01 | 0.00 | 1.06 | 0.18 | 0.01 | 0.72 | ||

Moundou | 4 | 0.09a | 0.71abc | 0.45a | 9.00 | 8.00bc | 4.00 | 7.55c | 3.13abc |

0.00 | 0.03 | 0.03 | 0.00 | 0.00 | 0.00 | 0.24 | 0.95 | ||

Afunori | 5 | 0.14cd | 0.73bc | 0.43 | 9.00 | 8.04bc | 4.40 | 7.52bc | 5.24d |

0.01 | 0.03 | 0.03 | 0.00 | 0.09 | 0.89 | 0.28 | 0.40 | ||

Maiadua | 3 | 0.15cd | 0.73bc | 0.44a | 9.00 | 8.00bc | 5.30 | 6.75abc | 4.10bcd |

0.01 | 0.02 | 0.00 | 0.00 | 0.00 | 0.25 | 0.07 | 0.00 | ||

Bauchi | 2 | 0.20e | 0.78c | 0.46a | 9.00 | 8.00bc | 4.00 | 6.45a | 2.65ab |

0.01 | 0.02 | 0.01 | 0.00 | 0.00 | 0.00 | 0.49 | 1.06 | ||

Mubi | 4 | 0.15cd | 0.69ab | 0.45a | 9.00 | 7.85abc | 4.00 | 6.68abc | 3.28abc |

0.00 | 0.04 | 0.02 | 0.00 | 0.03 | 0.00 | 0.59 | 0.34 | ||

Jos | 2 | 0.17de | 0.74bc | 0.44a | 9.00 | 7.40ab | 4.00 | 6.65abc | 3.80bcd |

0.01 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.21 | 0.28 |

^{*}Significant (p < 0.05); ^{**}highly significant (p < 0.01); ^{***}very highly Significant (p < 0.001); ^{†}not significant (p > 0.05); according to one-way ANOVA. Means within a column followed by the same letter are not significantly different at p = 0.05 according to Tukey HSD test. Hair: Cover hair on tergite 5; Tom1: Width of tomentum; Tom2: Width of stripe behind tomentum; Pt2, 3 & 4: Pigmentation of tergites 2, 3 & 4; Scut1,2: pigmentation of scutellum and its plates. Numbers in brackets are Ruttner numbers.

Locality | N | Femur, length(5)^{***} | Tibia, length(6)^{***} | Metatarsus, length(7)^{***} | Metatarsus, width(8)^{***} |
---|---|---|---|---|---|

Maga | 5 | 2.36a | 2.82a | 1.79a | 1.06ab |

0.03 | 0.08 | 0.03 | 0.02 | ||

Touboro | 4 | 2.45abc | 2.96ab | 1.87abc | 1.09bc |

0.02 | 0.05 | 0.04 | 0.01 | ||

N'Djamena | 3 | 2.40ab | 2.89ab | 1.83abc | 1.05ab |

0.03 | 0.05 | 0.03 | 0.01 | ||

Am Timan | 3 | 2.43abc | 2.94ab | 1.82abc | 1.07ab |

0.03 | 0.03 | 0.05 | 0.01 | ||

Bousso | 4 | 2.41abc | 2.91ab | 1.84abc | 1.07ab |

0.02 | 0.04 | 0.01 | 0.02 | ||

Sarh | 2 | 2.41abc | 2.92ab | 1.83abc | 1.07ab |

0.01 | 0.03 | 0.01 | 0.02 |

Moundou | 4 | 2.39ab | 2.94ab | 1.81ab | 1.08ab |
---|---|---|---|---|---|

0.02 | 0.04 | 0.02 | 0.02 | ||

Afunori | 5 | 2.37a | 2.89ab | 1.82abc | 1.04a |

0.03 | 0.04 | 0.03 | 0.02 | ||

Maiadua | 3 | 2.50c | 3.05b | 1.91c | 1.13c |

0.08 | 0.12 | 0.04 | 0.03 | ||

Bauchi | 2 | 2.45abc | 2.98ab | 1.88abc | 1.10bc |

0.01 | 0.00 | 0.05 | 0.02 | ||

Mubi | 4 | 2.41ab | 2.95ab | 1.85abc | 1.08ab |

0.02 | 0.04 | 0.04 | 0.01 | ||

Jos | 2 | 2.48bc | 3.01b | 1.89bc | 1.10bc |

0.00 | 0.01 | 0.00 | 0.00 |

^{***}Very highly significant (p < 0.001), according to one-way ANOVA. Means, within a column, followed by the same letter are not significantly different at p = 0.05 according to Tukey HSD test. Numbers in brackets are Ruttner numbers.

Locality | N | Lt3 (9)^{***} | Lt4 (10)^{***} | Lst3 (11)^{**} | Lwm (12) ^{†} | Wwm (13)^{**} | Dwm (14)^{†} | Lst6 (15)^{†} | Wst6 (16)^{*} |
---|---|---|---|---|---|---|---|---|---|

Maga | 5 | 1.93a | 1.88ab | 2.35ab | 1.19 | 1.98a | 0.31 | 2.20 | 2.68a |

0.01 | 0.01 | 0.04 | 0.02 | 0.05 | 0.02 | 0.06 | 0.04 | ||

Touboro | 4 | 1.97abc | 1.92abc | 2.48b | 1.23 | 2.06a | 0.30 | 2.26 | 2.78a |

0.03 | 0.04 | 0.02 | 0.01 | 0.03 | 0.03 | 0.05 | 0.05 | ||

N'Djamena | 3 | 1.97abc | 1.91abc | 2.38ab | 1.21 | 2.02a | 0.31 | 2.23 | 2.67a |

0.01 | 0.01 | 0.02 | 0.02 | 0.03 | 0.03 | 0.01 | 0.03 | ||

Am Timan | 3 | 2.04abc | 1.99bc | 2.43ab | 1.22 | 1.99a | 0.32 | 2.22 | 2.66a |

0.04 | 0.04 | 0.04 | 0.02 | 0.03 | 0.02 | 0.04 | 0.01 | ||

Bousso | 4 | 1.99abc | 1.93abc | 2.42ab | 1.22 | 1.98a | 0.31 | 2.22 | 2.66a |

0.03 | 0.03 | 0.04 | 0.03 | 0.04 | 0.01 | 0.05 | 0.06 | ||

Sarh | 2 | 1.98abc | 1.92abc | 2.43ab | 1.21 | 1.98a | 0.32 | 2.22 | 2.67a |

0.04 | 0.05 | 0.04 | 0.03 | 0.00 | 0.01 | 0.04 | 0.06 | ||

Moundou | 4 | 1.97abc | 1.92abc | 2.37ab | 1.19 | 1.98a | 0.30 | 2.23 | 2.70a |

0.06 | 0.06 | 0.02 | 0.03 | 0.05 | 0.00 | 0.04 | 0.04 | ||

Afunori | 5 | 1.94ab | 1.87a | 2.33a | 1.18 | 1.92a | 0.31 | 2.22 | 2.64a |

0.05 | 0.06 | 0.02 | 0.01 | 0.02 | 0.01 | 0.05 | 0.06 | ||

Maiadua | 3 | 2.07c | 2.01c | 2.46ab | 1.23 | 2.05a | 0.33 | 2.29 | 2.79a |

0.05 | 0.05 | 0.09 | 0.05 | 0.13 | 0.02 | 0.10 | 0.10 | ||

Bauchi | 2 | 1.99abc | 1.94abc | 2.41ab | 1.19 | 2.05a | 0.35 | 2.28 | 2.76a |

0.02 | 0.02 | 0.10 | 0.06 | 0.06 | 0.01 | 0.03 | 0.10 | ||

Mubi | 4 | 1.93a | 1.87a | 2.44ab | 1.22 | 2.05a | 0.30 | 2.28 | 2.79a |

0.03 | 0.03 | 0.07 | 0.04 | 0.03 | 0.02 | 0.05 | 0.06 | ||

Jos | 2 | 1.99abc | 1.93abc | 2.42ab | 1.20 | 2.06a | 0.33 | 2.23 | 2.77a |

0.03 | 0.03 | 0.04 | 0.01 | 0.05 | 0.01 | 0.03 | 0.01 |

^{*}Significant (p < 0.05); ^{**}highly significant (p < 0.01); ^{***}very highly significant (p < 0.001); ^{†}not significant (p > 0.05), according to one-way ANOVA. Means, within a column, followed by the same letter are not significantly different at p = 0.05 according to Tukey HSD test. Lt3, 4: Tergites 3, 4, longitudinal; Lst3: Sternite 3, longitudinal; Lwm: Wax mirror, longitudinal; Wwm: Wax mirror, width; Dwm: Distance between wax mirrors; Lst6: Sternite 6, longitudinal; Wst6: Sternite 6, width. Numbers in brackets are Ruttner numbers.

Locality | N | Fwl (17)^{***} | Fww (18) ^{†} | Cub-a (19)^{†} | Cub-b (20)^{†} | A4 (21) ^{†} | B4 (22)^{†} | D7 (23)^{*} | E9 (24)^{*} |
---|---|---|---|---|---|---|---|---|---|

Maga | 5 | 8.16ab | 2.77 | 48.82 | 22.62 | 32.94 | 101.16 | 102.79ab | 19.20ab |

0.10 | 0.05 | 3.76 | 1.88 | 1.06 | 3.39 | 1.69 | 0.63 | ||

Touboro | 4 | 8.36b | 2.81 | 45.11 | 21.20 | 33.34 | 105.63 | 103.10b | 18.79ab |

0.07 | 0.08 | 3.72 | 1.56 | 1.92 | 4.65 | 1.36 | 0.46 | ||

N'Djamena | 3 | 8.18ab | 2.81 | 46.66 | 22.99 | 33.42 | 103.31 | 103.00ab | 19.39ab |

0.12 | 0.11 | 3.01 | 0.44 | 1.38 | 2.22 | 1.27 | 0.52 | ||

Am Timan | 3 | 8.14ab | 2.76 | 49.67 | 20.51 | 33.91 | 97.57 | 101.16ab | 17.93a |

0.04 | 0.01 | 2.32 | 1.60 | 0.57 | 2.41 | 0.65 | 0.29 | ||

Bousso | 4 | 8.20abc | 2.79 | 49.19 | 21.66 | 33.30 | 100.13 | 100.50ab | 18.48ab |

0.05 | 0.04 | 1.72 | 1.60 | 1.12 | 3.35 | 0.92 | 0.90 | ||

Sarh | 2 | 8.10ab | 2.81 | 51.31 | 21.21 | 32.49 | 101.81 | 100.61ab | 18.40ab |

0.01 | 0.00 | 1.38 | 0.63 | 0.63 | 0.43 | 1.46 | 0.12 | ||

Moundou | 4 | 8.19ab | 2.77 | 50.59 | 19.95 | 31.93 | 102.12 | 100.16ab | 18.68ab |

0.09 | 0.04 | 2.72 | 1.35 | 0.33 | 1.05 | 0.75 | 0.32 | ||

Afunori | 5 | 8.04a | 2.77 | 48.90 | 21.10 | 32.13 | 103.63 | 101.18ab | 19.61ab |

0.14 | 0.06 | 4.25 | 1.04 | 0.67 | 1.65 | 1.77 | 0.98 | ||

Maiadua | 3 | 8.50d | 2.82 | 48.40 | 23.00 | 32.63 | 102.45 | 101.40ab | 19.40ab |

0.18 | 0.10 | 3.22 | 1.34 | 1.36 | 3.95 | 2.06 | 0.61 | ||

Bauchi | 2 | 8.47cd | 2.90 | 50.47 | 22.22 | 32.46 | 101.97 | 99.03a | 19.94b |

0.01 | 0.02 | 8.06 | 1.71 | 1.21 | 2.72 | 1.51 | 0.32 | ||

Mubi | 4 | 8.36bcd | 2.83 | 50.06 | 21.66 | 31.53 | 104.89 | 101.39ab | 18.84ab |

0.05 | 0.05 | 4.08 | 2.90 | 0.73 | 3.44 | 1.04 | 0.94 | ||

Jos | 2 | 8.56d | 2.90 | 54.92 | 22.24 | 31.36 | 103.69 | 100.14ab | 19.32ab |

0.03 | 0.04 | 4.03 | 0.82 | 0.41 | 0.24 | 1.89 | 0.65 |

Locality | N | G18 (25)^{†} | J10 (26)^{†} | J16 (27)^{***} | K19 (28)^{***} | L13 (29)^{†} | N23 (30)^{**} | O26 (31)^{†} |
---|---|---|---|---|---|---|---|---|

Maga | 5 | 97.26 | 51.92 | 93.21abc | 79.25abc | 14.92 | 88.18ab | 40.03 |

2.10 | 3.49 | 1.46 | 1.99 | 1.00 | 1.18 | 1.97 | ||

Touboro | 4 | 94.68 | 53.72 | 92.98abc | 80.48abc | 15.13 | 89.62ab | 39.92 |

3.41 | 4.00 | 2.03 | 2.39 | 0.70 | 1.97 | 2.10 | ||

N'Djamena | 3 | 95.91 | 51.04 | 93.29abc | 80.39abc | 15.73 | 87.64ab | 38.91 |

2.37 | 0.21 | 1.37 | 1.89 | 0.38 | 1.26 | 0.91 | ||

Am Timan | 3 | 95.24 | 51.42 | 96.94d | 83.28bc | 14.86 | 90.19ab | 39.04 |

1.12 | 0.13 | 1.20 | 1.08 | 0.30 | 1.02 | 0.63 | ||

Bousso | 4 | 94.61 | 50.57 | 97.51d | 83.23bc | 15.01 | 90.43b | 39.99 |

1.41 | 0.48 | 0.56 | 1.11 | 0.43 | 0.89 | 1.98 |

Sarh | 2 | 96.21 | 51.71 | 96.57cd | 82.46abc | 15.12 | 90.07ab | 40.04 |
---|---|---|---|---|---|---|---|---|

3.46 | 0.45 | 1.32 | 0.65 | 0.24 | 1.56 | 2.04 | ||

Moundou | 4 | 94.47 | 50.82 | 95.44bcd | 83.58c | 15.47 | 89.97ab | 38.24 |

1.13 | 0.33 | 0.75 | 1.08 | 0.44 | 1.11 | 1.76 | ||

Afunori | 5 | 94.17 | 52.51 | 90.11a | 79.29bc | 16.04 | 86.18a | 36.86 |

2.04 | 0.51 | 1.34 | 2.02 | 0.71 | 1.98 | 2.42 | ||

Maiadua | 3 | 95.78 | 53.20 | 93.25abc | 78.43a | 15.04 | 88.06ab | 38.94 |

1.45 | 1.41 | 0.87 | 0.54 | 0.79 | 1.17 | 3.43 | ||

Bauchi | 2 | 95.07 | 52.55 | 95.05bcd | 78.97ab | 15.01 | 87.15ab | 39.26 |

0.99 | 0.42 | 0.96 | 0.03 | 0.89 | 0.94 | 2.16 | ||

Mubi | 4 | 96.72 | 53.10 | 92.85ab | 80.07abc | 16.34 | 87.35ab | 38.06 |

1.32 | 0.99 | 1.28 | 0.49 | 1.41 | 1.95 | 1.38 | ||

Jos | 2 | 92.77 | 50.74 | 92.82ab | 79.59abc | 15.17 | 86.57ab | 40.65 |

2.79 | 0.17 | 0.94 | 1.63 | 0.28 | 0.11 | 3.18 |

^{*}Significant (p < 0.05); ^{**}highly significant (p < 0.01); ^{***}very highly Significant (p < 0.001) and ^{†}not significant (p > 0.05), according to one-way ANOVA. Means, within a column, followed by the same letter are not significantly different at p = 0.05 according to Tukey HSD test. Measurements of distance are in mm and of angles in degrees. Fwl: Fore-wing, length; Fww: Fore-wing, width; Cub-a, b: Cubital vein, distance a, b; A4-O26: 11 angles of wing veins. Numbers in brackets are Ruttner numbers.

failure to meet some conditions) of 10 worker honeybees from each of 42 colonies at 13 localities, was run to detect possible clusters. The suitability of PCA was assessed prior to analysis. Inspection of the correlation matrix showed that all variables had the minimum requirement of at least one correlation coefficient greater than 0.3. The overall Kaiser-Meyer-Olkin (KMO) measure was 0.68 with individual KMO measures from 0.53 to 0.82, thus meeting the minimum requirement for sampling adequacy. Bartlett's test of sphericity was statistically significant (p < 0.0005), suggesting that the data could be appropriately analysed using PCA [

Three principal components, with eigenvalues 2.97, 1.23 and 0.72 each and accounting for 81.57% of the total variance were extracted. A Varimax orthogonal rotation was employed to aid interpretability. There were strong loadings of characters of size on all three components and pigmentation of plates of scutellum on component 2 (

As may be seen in

Since PCA did not produce a clear clustering of the colonies, an alternative method, hierarchical cluster analysis, using means of 35 morphometric characters for the 13 localities under investigation, was used. Based on the output of this analysis (

A stepwise discriminant analysis (DA) was run, in order to predict the membership of the 42 colonies of A. mellifera, among the three a priori groups defined by the cluster analysis, as a means of confirming these groups. 35 morphometric characters of workers were used as predictor variables. Significant mean differences (ANOVA; p < 0.05) were observed for all, but 12, of the variables. While the log determinants were similar (−9, −10 and −11, respectively, for the three groups), Box’s M indicated that the assumption of equality of covariance matrices was not violated (p > 0.05). Thus, DA was deemed appropriate [

Two canonical discriminant functions (with eigenvalues 4.6 and 3.4, respectively) were used in the analysis. They explained 57.8% and 42.2% of the total variance, respectively, and their Wilk’s Lambda values, assessed by

Character (Ruttner numbers) | Rotated Component Coefficients | Communalities | ||
---|---|---|---|---|

Component 1 | Component 2 | Component 3 | ||

Metatarsus, length (7) | 0.835 | 0.400 | 0.86 | |

Metatarsus, width (8) | 0.539 | 0.410 | 0.460 | 0.67 |

Fore wing, width (18) | 0.908 | 0.87 | ||

Sternite 3, longitudinal (11) | 0.512 | 0.620 | 0.70 | |

Pigmentation of plates of scutellum (36) | -0.920 | 0.87 | ||

Tergite 4, longitudinal (10) | 0.930 | 0.91 |

Case | Squared Euclidean Distance | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|

1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | |

1: Afunori | 0 | 112 | 104 | 84 | 109 | 97 | 47 | 139 | 52 | 66 | 45 | 73 | 122 |

2: Am Timan | 112 | 0 | 90 | 15 | 104 | 70 | 81 | 96 | 43 | 88 | 68 | 35 | 84 |

3: Bauchi | 104 | 90 | 0 | 70 | 35 | 72 | 100 | 53 | 83 | 57 | 83 | 63 | 85 |

4: Bousso | 84 | 15 | 70 | 0 | 75 | 46 | 52 | 93 | 31 | 64 | 43 | 23 | 66 |

5: Jos | 109 | 104 | 35 | 75 | 0 | 74 | 111 | 69 | 79 | 62 | 86 | 57 | 91 |

6: Koumra | 97 | 70 | 72 | 46 | 74 | 0 | 55 | 90 | 52 | 51 | 48 | 45 | 55 |

7: Maga | 47 | 81 | 100 | 52 | 111 | 55 | 0 | 131 | 53 | 69 | 21 | 53 | 93 |

8: Maiadua | 139 | 96 | 53 | 93 | 69 | 90 | 131 | 0 | 111 | 75 | 93 | 89 | 75 |

9: Moundou | 52 | 43 | 83 | 31 | 79 | 52 | 53 | 111 | 0 | 54 | 42 | 30 | 94 |

10: Mubi | 66 | 88 | 57 | 64 | 62 | 51 | 69 | 75 | 54 | 0 | 46 | 51 | 51 |

11: N'Djamena | 45 | 68 | 83 | 43 | 86 | 48 | 21 | 93 | 42 | 46 | 0 | 46 | 68 |

12: Sarh | 73 | 35 | 63 | 23 | 57 | 45 | 53 | 89 | 30 | 51 | 46 | 0 | 78 |

13: Touboro | 122 | 84 | 85 | 66 | 91 | 55 | 93 | 75 | 94 | 51 | 68 | 78 | 0 |

chi-square, were highly significant (p < 0.0005), suggesting they had sufficient discriminatory power to group the cases. The discriminant variables used in the analysis and their correlations with the discriminant functions are shown in

Overall, 95% of cross-validated grouped cases were correctly classified. 13 of the 15 cases in cluster 1 were classified with a posterior probability of at least 95% while 12 of the 13 cases in cluster 2 were also classified

Variable (Ruttner Number) | Function | |
---|---|---|

1 | 2 | |

Length of cover hair on tergite 5 (1) | 0.331^{†} | 0.280 |

Wing venation angle B4 (22) | 0.304 | 0.080 |

Wing venation angle J16 (27) | −0.463 | 0.380 |

Fore-wing, length (17) | 0.370 | 0.543 |

Wing venation angle G18 (25) | 0.049 | −0.062 |

Pigmentation of plates of scutellum (36) | 0.298 | −0.613 |

^{†}The largest absolute correlation between each variable and any discriminant function is shown in bold.

with the same posterior probability. For cluster 3 all, but one of the 13 cases, were as well classified with a posterior probability of 95% and above.

A pairwise comparison of the groups, using F-statistic, revealed a very highly significant difference between the groups' centroids (p < 0.0005). A scatter plot of the two discriminant functions is shown in

A Pearson’s product-moment correlation analysis was run to assess the relationship between latitude, longitude and altitude and principal component 1 extracted by PCA and loaded with characters of body size. Preliminary analyses showed the relationship to be linear with all variables normally distributed (as assessed by visual inspection of normal Q-Q plots) and all outliers were removed [

In order to isolate the effect of longitude on the relationship between altitude and principal component 1, and vice vasa, the relationship of either variable with principal component 1 was subjected to a first-order partial correlation, controlling for the effects of the other. The correlation between altitude and principal component 1, controlling for longitude, was statistically significant (r (29) = 0.371, p < 0.05) indicating that a relationship between altitude and principal component 1 exists above and beyond the effects of longitude. On the other hand, the correlation between longitude and this component, controlling for altitude, was not statistically significant (r (29) = 0.255, p > 0.05), indicating that a relationship between longitude and principal component 1 does not exist above and beyond the effects of altitude. This underscores the importance of altitude in the variation of size of bees in the Lake Chadic basin (

As may be seen in

The trend observed in this study, in which the size of the bees increases with altitude, was similarly reported from East Africa [

Based on the agreement between the results of this study and those of previous studies, it is concluded that the honeybees of this area are morphometrically pure populations of sub-Saharan A. mellifera.

Character | This study | Ruttner [ | Ajao et al. [ | Yu et al. [ | Oyerinde et al. [ |
---|---|---|---|---|---|

Cover hair, length | 0.09 ± 0.00 - 0.20 ± 0.01 | 0.20 ± 0.02 - 0.26 ± 0.04 | |||

Fore-wing, length | 8.04 ± 0.14 - 8.56 ± 0.03 | 8.13 ± 0.19 - 8.95 ± 0.37 | 9.54 ± 0.01^{†} | 8. 42 ± 0. 66 | 3.43 ± 0.16^{†} |

Fore-wing, width | 2.71 ± 0.04 - 2.77± 0.06 | 3. 13 ± 0. 21 | 1.18 ± 0.08^{†} | ||

Tergites 3 + 4, diameter | 3.81 ± 0.01 - 4.09 ± 0.05 | 3.92 ± 0.10 - 4.25 ± 0.21 | 3. 80 ± 0. 28 | ||

Angle J16 | 90.11 ± 1.34 - 97.51 ± 0.56 | 86.44 ± 8.37 - 96.76 ± 3.60 | |||

Pigmentation, scutellum | 6.40 ± 0.41- 7.60 ± 0.17 | 0.35 ± 0.73 - 6.77 ± 0.96 |

^{†}The correctness of these values is doubtful because they fall outside the range reported for all subspecies of A. mellifera. For example, in respect of the length of the fore-wing, the smallest value, 8.13 ± 0.19 mm, was reported for A. m. jemenitica and the highest value, 9.33 ± 0.11 mm, for A. m. mellifera [

^{1}Sources: [

I wish to express my sincere gratitude to Ms. Beate Springer of Institut für Bienenkunde, Oberursel, for her assistance in dissections and measurements and to the Institute for providing the facilities. My special thanks go to the numerous beekeepers, honey hunters, public servants, traditional rulers, my former students, friends and other well-wishers for their support during my fieldtrips in Nigeria, Cameroon and Chad. The study was partially funded by the federal government of Nigeria through TETFUND and Abubakar Tafawa Balewa University.

Usman H. Dukku, (2016) Evaluation of Morphometric Characters of Honeybee (Apis mellifera L.) Populations in the Lake Chad Basin in Central Africa. Advances in Entomology,04,75-89. doi: 10.4236/ae.2016.42009